Well, I finished Doom Eternal on Nightmare (hardest difficulty that isn't deathless) plus all the DLC and Slayer Gates. Here's my review on everything:

Gameplay
-------------------------
Doom Eternal is the pinnacle of FPS combat. It's a game that truly tries seasoned veterans of the genre and forces them to adapt and survive, while providing intense adrenaline rushes and feeling like an arena shooter. It's extremely punishing and extremely rewarding.
Eternal encourages using your entire arsenal in-game with its cast of enemies and their design, as well as the arenas. Certain enemies have certain weaknesses to certain weapons, which promotes you switching weapons all the time to do insane weapon combos to take out tough enemies. Minus a couple weapon mods (which they manage to make useful in the DLC), everything has a specific place and purpose. That's not to say that the base gameplay loop is repetitive with you using the same tool for every job when you fight a specific enemy. There's not only one way to take out every enemy in Doom Eternal. Proof of this can be found in some of the super skilled players that you can find on YouTube (and some videos discussing the topic can be found at Under The Mayo's channel).
Enemies are varied, with intelligent AI on every single one of them as well as insane damage. Even base fodder can kill you in two to three hits. However, the game gives you all the tools necessary to dispose of said enemies as well as dodge and avoid them.
Arenas are designed purposefully, encouraging movement by providing open or closed areas with several chokepoints. Combined with the enemy AI, every arena is turned into an extremely tense firefight and chase sequence while you attempt to dodge and weave while slowly chipping away at the horde.
In between arenas, there are frequently platforming sections that try to help you practice your platforming skills in preparations for use in arenas. Most of these are relatively easy to figure out and understand. A lot of people don't like these sections, but they're really not a bother and enhance Doom Eternal overall.
Sometimes, there are sections that serve more as just pure ambience or introductions to levels. They set the mood well while providing beautiful, inventive, and varied landscapes.

In Eternal, checkpoints are often and between each arena, and provided you have an SSD, loading times are fast so dying every time isn't that big of a deal. I wish there could be no loading screen at all, but I really can't complain when the game runs so well.
There are secrets to find all over, including lore, toys, cheat codes, etc, which are all viewable in your home base, the Fortress of Doom. In case you miss some earlier in the level, at the end of every level, you can Fast Travel to certain sections of the maps to grab any secrets you may have missed.
As well as guns you gain over time in Eternal's story, you are also able to gain skill points and runes to have passive or active abilities both on Doomguy and your weapons to improve your demon-slaying capabilities. These are earned by completing battles, both in the main story, secret encounters, and Slayer Gates (optional super hard arenas). You can also "master" weapons by completing a challenge. You will unlock a certain ability by doing it, ranging from extremely useful to the point of it becoming a regular part of your combos to having little impact on your overall playstyle. (The ones that really matter are usually pretty easy though).
The map system from 2016's Doom is improved upon drastically by becoming clearer and easier to navigate. I use it regularly and it Just Werks­™.
Tutorials are often shoved in your face to explain how enemies work and how to defeat them, as well as weakpoints. While this is good sometimes, it's not good all the time. I suggest keeping the tutorials off for everything past the first half of the base game, and referring to your codex should you need it.

Overall, the core gameplay loop of Doom Eternal, as well as the extra systems, are all purposefully designed to add to the experience through the use of maps, weapons, enemies, etc. You can feel yourself becoming more powerful and deadly over time. It's very satisfying, but takes a minute to get most of the arsenal and really get into what Eternal is about.

Music
-------------------------
In case you don't know, Doom is a series famed for its legendary soundtracks, even moreso now with the introduction of Lead Composer Mick Gordon in 2016's Doom. Mick Gordon combines EDM, heavy metal, throat singing, and a bunch of other genres that I'm too stupid to understand to create another legendary soundtrack. While I would argue that 2016's Doom has a better overall soundtrack, Eternal has some highlights and still holds up on its own very well. Both enhance the gameplay by making you feel like a total badass and adding to the scene, which is really all you could ask for.

Graphics
-------------------------
This game is one of the most gorgeous games I've played, and it runs like butter even WITH raytracing on. I never get dropped frames, I never get lagged out, and it's just perfect. The artstyle works really well, and enemy designs are thematically appropriate but distinct, so you know what you're fighting when you try and go for an enemy.
Some of the skyboxes are the most awe-inspiring things I've ever seen. The sheer scope and scale Doom Eternal is able to convey is staggering, and I commend the art team and developers for being able to create something so beautiful that runs on potato hardware.

Story
-------------------------
Story is not important to me in a Doom game. If you're interested in that, there are codex pages you can pick up which explain the lore as well as in-game cutscenes and the occasional narration by friend or foe. What matters to me is that it creates badass scenarios, and it definitely delivers.
There are a couple over-the-top moments that make you cringe a tiny bit, but they're not that bad. You're able to feel like an absolute badass but not the Shadow the Edgehog kind.

Replayability
-------------------------
Has a good bit of replayability IMO, but it's not something I want to replay. I got what I wanted out of Doom Eternal, and I want nothing more. If you want to play more though, there are community rulesets, apparently there are campaign mods, Master Levels (aka current levels that are officially remixed with different enemies to be extra challenging), and the base game with cheat codes and different difficulties.


A couple things to keep in mind if you decide to play:
1) If you play FPSes regularly enough to think of yourself as somewhat decent, you need to try Nightmare difficulty. It is the best way to play Doom Eternal.
2) Experiment. Try weird things out that you think might work. It could elevate your gameplay.
3) The Marauder isn't badly designed.

Overall, I wholeheartedly recommend this game. At full price? Sure. But it goes on sale so often that you'd be shooting yourself in the foot by not waiting for a sale.
I had fun, and I hope you do too.

Well, I finished Doom Eternal on Nightmare (hardest difficulty that isn't deathless) plus all the DLC and Slayer Gates. Here's my review on everything: Gameplay ------------------------- Doom Eternal is the pinnacle of FPS combat. It's a game that truly tries seasoned veterans of the genre and forces them to adapt and survive, while providing intense adrenaline rushes and feeling like an arena shooter. It's extremely punishing and extremely rewarding. Eternal encourages using your entire arsenal in-game with its cast of enemies and their design, as well as the arenas. Certain enemies have certain weaknesses to certain weapons, which promotes you switching weapons all the time to do insane weapon combos to take out tough enemies. Minus a couple weapon mods (which they manage to make useful in the DLC), everything has a specific place and purpose. That's not to say that the base gameplay loop is repetitive with you using the same tool for every job when you fight a specific enemy. There's not only one way to take out every enemy in Doom Eternal. Proof of this can be found in some of the super skilled players that you can find on YouTube (and some videos discussing the topic can be found at Under The Mayo's channel). Enemies are varied, with intelligent AI on every single one of them as well as insane damage. Even base fodder can kill you in two to three hits. However, the game gives you all the tools necessary to dispose of said enemies as well as dodge and avoid them. Arenas are designed purposefully, encouraging movement by providing open or closed areas with several chokepoints. Combined with the enemy AI, every arena is turned into an extremely tense firefight and chase sequence while you attempt to dodge and weave while slowly chipping away at the horde. In between arenas, there are frequently platforming sections that try to help you practice your platforming skills in preparations for use in arenas. Most of these are relatively easy to figure out and understand. A lot of people don't like these sections, but they're really not a bother and enhance Doom Eternal overall. Sometimes, there are sections that serve more as just pure ambience or introductions to levels. They set the mood well while providing beautiful, inventive, and varied landscapes. In Eternal, checkpoints are often and between each arena, and provided you have an SSD, loading times are fast so dying every time isn't that big of a deal. I wish there could be no loading screen at all, but I really can't complain when the game runs so well. There are secrets to find all over, including lore, toys, cheat codes, etc, which are all viewable in your home base, the Fortress of Doom. In case you miss some earlier in the level, at the end of every level, you can Fast Travel to certain sections of the maps to grab any secrets you may have missed. As well as guns you gain over time in Eternal's story, you are also able to gain skill points and runes to have passive or active abilities both on Doomguy and your weapons to improve your demon-slaying capabilities. These are earned by completing battles, both in the main story, secret encounters, and Slayer Gates (optional super hard arenas). You can also "master" weapons by completing a challenge. You will unlock a certain ability by doing it, ranging from extremely useful to the point of it becoming a regular part of your combos to having little impact on your overall playstyle. (The ones that really matter are usually pretty easy though). The map system from 2016's Doom is improved upon drastically by becoming clearer and easier to navigate. I use it regularly and it Just Werks­™. Tutorials are often shoved in your face to explain how enemies work and how to defeat them, as well as weakpoints. While this is good sometimes, it's not good all the time. I suggest keeping the tutorials off for everything past the first half of the base game, and referring to your codex should you need it. Overall, the core gameplay loop of Doom Eternal, as well as the extra systems, are all purposefully designed to add to the experience through the use of maps, weapons, enemies, etc. You can feel yourself becoming more powerful and deadly over time. It's very satisfying, but takes a minute to get most of the arsenal and really get into what Eternal is about. Music ------------------------- In case you don't know, Doom is a series famed for its legendary soundtracks, even moreso now with the introduction of Lead Composer Mick Gordon in 2016's Doom. Mick Gordon combines EDM, heavy metal, throat singing, and a bunch of other genres that I'm too stupid to understand to create another legendary soundtrack. While I would argue that 2016's Doom has a better overall soundtrack, Eternal has some highlights and still holds up on its own very well. Both enhance the gameplay by making you feel like a total badass and adding to the scene, which is really all you could ask for. Graphics ------------------------- This game is one of the most gorgeous games I've played, and it runs like butter even WITH raytracing on. I never get dropped frames, I never get lagged out, and it's just perfect. The artstyle works really well, and enemy designs are thematically appropriate but distinct, so you know what you're fighting when you try and go for an enemy. Some of the skyboxes are the most awe-inspiring things I've ever seen. The sheer scope and scale Doom Eternal is able to convey is staggering, and I commend the art team and developers for being able to create something so beautiful that runs on potato hardware. Story ------------------------- Story is not important to me in a Doom game. If you're interested in that, there are codex pages you can pick up which explain the lore as well as in-game cutscenes and the occasional narration by friend or foe. What matters to me is that it creates badass scenarios, and it definitely delivers. There are a couple over-the-top moments that make you cringe a tiny bit, but they're not that bad. You're able to feel like an absolute badass but not the Shadow the Edgehog kind. Replayability ------------------------- Has a good bit of replayability IMO, but it's not something I want to replay. I got what I wanted out of Doom Eternal, and I want nothing more. If you want to play more though, there are community rulesets, apparently there are campaign mods, Master Levels (aka current levels that are officially remixed with different enemies to be extra challenging), and the base game with cheat codes and different difficulties. A couple things to keep in mind if you decide to play: 1) If you play FPSes regularly enough to think of yourself as somewhat decent, you need to try Nightmare difficulty. It is the best way to play Doom Eternal. 2) Experiment. Try weird things out that you think might work. It could elevate your gameplay. 3) The Marauder isn't badly designed. Overall, I wholeheartedly recommend this game. At full price? Sure. But it goes on sale so often that you'd be shooting yourself in the foot by not waiting for a sale. I had fun, and I hope you do too.