*PLEASE NOTE that this campaign was played with the Left 4 Bots (Improved A.I.) and Smart Bots addons. It made possible for the bots to walk through the underwater section no problem (You have to walk away to the next room, otherwise they fall back into the water when they reach the surface as they all are trying to climb at the same time, eventually they will go out and stop falling back in)

Chapter 1 is well designed and balanced, backtracking is doable and the tight corridors make both for a balanced and fair experience at the same time of being a somewhat claustrophobic and stressful one, the only "complaint" I have is that is way too short, OTOH I LOVED the use of dynamic weather (you get in and it's regular foggy weather, then in the middle of the playthrough a storm starts).
Chapter 2 has similar traits to C1, this chapter is longer than that one and is pretty effing good as it is.

C1&2 I would give them around 8-9/10

C3, is fundamentally flawed in 4 ways:

1. It has Dynamic Paths that can and will be confusing because there are no arrows or anything to signal the current correct path

2. There is a series of Dynamic Events, meaning that in some playthroughs, some paths will be blocked but the related events won't be hidden even though they should in order to actually feek dynamic, creating confusion in new players, i.e: There is a point where you reach a lift, it has a shutter door at the right which will be either open or closed, and there will or not be a fence blocking access to said lift respectively, regardless of whether the access is or not blocked, if you have the Game Instructor on, you will see a "Raise the lift" instruction, which is impossible to do if the shutter is open and the lift is locked out of bounds.

*Bots might also get stuck in the first dynamic path but only if the player is dead (the AI addons allow the bots to continue by themselves).

2.1 If the shutter is open and the fence is present, bots will not be able to walk through the area and will be stuck going out and inside the room once you go past the gate.

3. There are 2 rooms full of explosive barrels, the first of them can be disabled by shooting at the walls before reaching it (in case the dynamic paths send the player through that route) but the second one can only be disabled if the Director is not sending the player through that route, making it a real PITA if you have to go through it (this happens when you can raise the lift) because you have to tell the bots to wait, have them actually wait, clean the room without blowing any barrels and make your way out without a horde spawning to have the bots follow you safely, or alternatively you can shoot the barrels and hope for the bots not to stop waiting until the fire has stopped or backtrack to them after shooting the barrels.

The first of them is located behind the 3 pipes [and approx 2 pipes in size to the left as well] that are in front of the torn apart shutter in the first interior, it can also be shot right after going out of the first interior, it's the aluminum wall in the left, it has a "FLAMMABLE" sign, and it can also be seen in front of the big stationary gas tank that can be reached via the first dynamic path (after going out and around the first interior with the torn up shutter and going up on the first ladder), there can be a hole in the wall or an open shutter or nothing at all), it has a red flammable sign on the dynamic path side.

If there is nothing in the first two possible paths, you must go through the door that is right before the mentioned ladder and down the ducts in that room, when coming out of the ducts, the player is in said room so it's better to shoot the wall just left of the 3 pipes as soon as going into the first interior of the platform or the external wall after going out of the first interior, this way when you arrive at the room all the barrels have already exploded)

The second room is right behind the "Raise the lift" lift, as indicated by the "FLAMMABLE" signs, if the shutter is open, the aluminum wall on the left is that room as well but being a bigger room, not all the barrels burn if you shoot at one of the extremes of the wall, better shoot all the wall area to be sure, but given that if the shutter is open you can't go into the room, it makes it useless to shoot at them)

4. Bugs: I have mentioned a couple already in the form of dynamic events but a game breaking one is that a certain combination of Dynamic Paths and Events let the survivors reach and interact with the console that turns off the alarm before turning the alarm on, and if said console is interacted with before turning the alarm on, once the alarm is turned on and the console is reached again, the alarm will not turn off, making it near impossible to reach the safe house.

There is an alleyway (last turn before the safe room) that drains health if you touch the fence (I see it's High Voltage but it just comes out as strange, annoying or unfair) and to be quite frank I thought it was a bug at first

C3 deserves a plain 3/10 as it has to be experienced many times before knowing all its quirks, once you know them, if you still don't hate and have given up on the campaign I think it deserves a 7/10

Finale is intense, in fact too intense, the first tank spawns when one's collected around 3/4 gas cans (3 if going for the two gas cans on top of the platform at first, which makes the most sense as the hordes make it near impossible to go down without losing a teammate or dying yourself if you go later on), then a couple minutes later you have TWO tanks spawn, then again one and two respectively, YES a finale with 6 tanks (4 or probably 3 if playing with competent humans), all while CI are swarming you.

C4 deserves a solid 8/10. That is ignoring the fact that the zombie spawn points massively suck in two points in this map: one at the very top of the tower with CI spawning in front of you right before you can take the gas AND SI spawning one "floor" above, meaning that hunters, jockeys, chargers will insta pin you, and if you left the bots waiting down below (which makes sense given what I previously mentioned, good luck not getting your team totally GM'd either by trying to rescue you or by taking fall damage.
The second heinous spawn point is 3 feet left of the pouring spot in the Generator, with zombies spawning in plain sight sometimes literally on top of you, just comes as the laziest level design option, equivalent to making enemies be bullet sponges to artificially increase the difficulty.

There is a bug in C4 where the gas counter never appears and the scavenge sequence doesn't start

Taking all that into account, C4 is a 5/10, an intense 5/10.

The campaign overall is good and I'd love to see those issues be ironed out honestly (I understand this was last updated in 2013), the idea is solid and the potential is there, it just needs some love

Verdict: 6.5-7/10