This mod was very interesting and ambitious when I came across it. Unfortunately it falls flat on its face in almost every aspect. It tries to do everything, and in doing so does nothing particularly well. If there is one piece of advice I can give to the dev, it's stop trying to do everything all at once. Slow down, and focus on making sure that each thing you make is good.

I played this as a single player experience on Heroic difficulty. I did not complete the entire campaign.

The game starts you off in a character creation mode which is really weird. I don't hate it, but feels very clunky and I'd honestly just rather use my own Spartan than a list of preset options. Nevertheless, there's a decent number of options to choose from and some mildly interesting choices.

You're then put into an armory where you can choose your starting weapons. I like this, you have the entire arsenal of human weapons to choose from.

Next you're given some options to change the way the game is played. One of the options is a day night cycle. I don't know why this is in the game, as night time is abhorrently awful. It's not actual night, you can see the sun still in the sky. Thee just down the gamma or brightness which in turn makes everything that glows feel like a flashlight right into your retinas. Another option is to skip the initial on rails mission. This should always be skipped by default. This mission is a waste of time and goes on for far, far too long. It serves no purpose, and it's extremely boring. The last option is the ability to either play in a sandbox mode, or the campaign mode. I played campaign. Here's where my review will start getting in depth.

The Map
Sandtrap is the map the dev chose for their mod. It's one of the biggest maps on Halo 3 so it's a fitting choice. Unfortunately this has its drawbacks, as because the map is so big, dropships will often deploy troops on the other side of the map, forcing you to either leave your entrenched position to find them, or wait till they come to you. This is always a problem, as a lot of time is wasted just waiting for the enemies to saunter up towards your position, or waiting for that last group of 5 to reveal themselves so that you could finally get on to the next wave.

The background has a UNSC ship and a Covenant ship linger on opposite sides as well as a flurry of air ship activity with banshees, hornets, and dropships all fighting each other. This is a neat addition, though I would like if the Covenant ships not appear on your radar from time to time. There is also what I think is High Charity crash landed in the background too, but it's so close to the foreground that it appears insanely small. Like you can actually nearly walk up to it. This thing is supposed to be hundreds of kilometres in diameter and height.

Across the map are plenty of weapons and ammo for you to scavenge whenever your initial weapons run out of ammo. They are all placed in intuitive areas and easy to reach and access. There are no vehicles that spawn, and there are some explosive barrels scattered here and there.

The Story
This is an extremely cringy fan-fiction level of writing and storytelling. As I didn't finish the entire campaign, I can't speak on exactly what happens past a certain point, but the gist appears that time travel is involved which explains why you're able to fight the various factions that show up.

At the very beginning you're met with an AI who assures you that he is totally not evil like Cortana was and that you can trust him, because he is part of the ship and can control the life support? The dialogue in this mod is next level bad. Everything sounds like it was written by a high schooler trying out creative writing for the very first time but doesn't understand how certain factions in his favorite game should be speaking. There is a Brute leader of the Banished that talks to you like he's some MCU villain with these extremely cringy lines that just take you out of the experience.

There's a moment in the mod where I think the AI tells you that there's some weird stuff going on and I kid you not the writing goes something like this, "We're finding people that should not be here. The people you're fighting, they shouldn't be here. There's definitely something going on. Oh, and some of the guys that you're seeing, they definitely should not be here. Something strange is happening where these groups of human and Covenant just should not be here."

The voice acting is amateur at best with obvious pitch shifts and extremely weak deliveries of certain lines. Everyone is monotone where even the most shocking of situations is met with bland uninteresting deliveries.

The Waves
Waves normally begin with a few Banished dropships unloading troops in various positions. Most of these enemies consist of Grunts and Brutes, though Jackals and Elites are present often enough as well. Every wave there is a chance for an 'event' to spawn. These events change up what you end up fighting. There's a mix bag of decent waves to waves that are just kill joys.

Specifically the Gravemind event is probably the worst event of all. The Gravemind shows up and can shoot you with very fast bolts of flood rockets that deal tons of damage and can easily kill you in a single volley. Normally this wouldn't be too much of a problem but what ends up happening is that like, 10 tentacles spawn up in a ring around the entire map and you have to kill them all to progress the event. Each tentacle has a ton of health and the Gravemind moves around the map so that you never really have a safe place to take out the tentacles, especially if you don't have a vehicle to ferry you around.

Other waves can include things like all invisible Elites, a 3 or 4-way battle between different factions, all charging Brutes, Sentinels, etc. The amount of variety is decent, though some of them really need to be looked at and changed.

After every round you're given a choice of reward from three options. This can range from a special weapon, reinforcements, or a vehicle. I do like this, but selecting an option feel clunky and needs to be more responsive. Early wave clears give you weak rewards, like a Mongoose or single use weapon, where waves near the end of the round will give you higher tier rewards like a an actual Warthog or special Spartan teammates. Each reward is random. This is a cool feature, though the rewards can feel underwhelming.

The Enemies
This mod ports over every single enemy from most Halo games. Heretics, Banished, Flood, Prometheans, and even Insurrectionists. This is a neat idea, but is kind of stifled because you can easily tell many of these enemies are just reskins of existing models and don't behave like how they should from their original game. Still though I appreciate the work dedicated to trying to being everything into this mod.

What drives me up the wall is how much extra health are given to everything. Every single enemy feels like a bullet sponge, that or every weapon feels extremely nerfed which I'll talk about later. Grunts have helmets that you have to shoot off first in order get a headshot on them. Why? Why would you ever do that? The Flood Juggernaut will expend every single bullet on the map before it goes down, and everything else just feels like it takes so much longer to kill than it does normally.

Since this is Halo 3, Elites were not meant to be enemies, and as such they tend to wig out quite a bit, throwing grenades at every single chance they get. A lot of new enemies like Jackal Skirmishers tend to act really funky too.

There's a Scarab fight at the very end of the final round, which just sucks. The campaign scarabs are placed in arenas that would allow you all kinds of different ways to get aboard and take it down. There have been times in this mod where the Scarab would just sit in the minefield or be angled in such a way that no matter what I physically could not jump onto it.

The Guns
Like the enemies, this mod aims to port over every single gun from every halo game. This was a terrible idea. Every single weapon in this mod, and somehow even the vanilla Halo 3 weapons, feel awful to use. All the rifles have terrible accuracy and damage. All the pistols are completely useless. Shotguns cannot damage anything beyond point-blank range. Snipers feel mostly fine, except most enemies require at least 2 shots to kill them, even with headshots. Somehow they made it feel like SMG and plasma pistol has the most damage potential from all the weapons available. There are legit some Brute enemies that can tank an entire Spartan Laser shot. Why in the world did you allow this to happen?

Every single gun ported from a different game just does not represent what that gun is supposed to be. Every single one is a duct-taped piece of parts slapped together to get a general sense of what that gun was supposed to be, and none of them feel good to use. Not even the skewer from Halo Infinite. They don't have the right sounds, the right feedback, the right looks, and especially not the same effects. I would so much rather prefer the dev to just have the Halo 3 guns, and then slowly add in the rest of the guns once each and every one is a perfect representation of what they're supposed to be.

The Vehicles
Don't bother. None of them are fun to use. They've all been nerfed into the ground to be extremely easy to die in and simply just do not do any damage. For some reason the dev hates fun and if you manage to get a flying vehicle you're limited to the amount of time you can use it, otherwise the game sends a kill squad to eliminate you. Why? Let me fly the hornet for as long as I can, it's a single player game and the enemies already have ways to kill me. I didn't play long enough to get a Scorpion but I can imagine it's just as worthless as the rest of the vehicles.

Maybe the warthogs have better use if you're playing multiplayer, but the AI just don't do a good enough job at shooting or driving to justify risking death to use it.

Conclusion
There's definitely more I can go into but I think my point has been made. This is a mod that seems really awesome but has a death of a thousand cuts of just bad decisions and poor execution. It seems as if the dev wants to shove as much as he can into the mod without polishing anything.