Give me suggestions for good coop fps games (2 people only)

Borderlands 2 is amazing

Doom

Coop Storydriven isnt that much out there, Borderlands 1, 2 and the pre-sequel are great, as mentioned before.
You could also try Call of Duty World at war (the only call of duty where you can play the whole campaign together)
Payday 1 and 2 are good coop games, but they can tend to be grindy and therefore not tht much fun. Killing Floor 1 and 2 are more like an arena shooter, but is a lot of fun together.
For Puzzles try Portal or for a industrial style you can try factorio.
If you like survival there are more variations, for example Ark, Pix-ark, Dark and Light, Conan exiles or 7 days to die

For Building there are games like Trailmakers, Besiege, Space Engineers, medival Engineers or Avorion.

It simply depends on what you like more

Borderlands 2 +1, or destiny 2

Killing floor 2 is excellent if you'd stretch your coop into "a team with common goal". It might sound like it's the same, but not quite.

Payday 2 is a lot of fun in my opinion :)

System Shock 2!

https://co-optim.us/16JHsI4

I can't really say much about the sequels (since I didn't play them) but I l played Sniper Elite II with a friend and it was quite fun.

It's an older game, but Return to Castle Wolfenstein with the rtcwcoop mod is a lot of fun. Also an older title, Duke Nukem 3D is my favorite old school shooter. I'd recommend the eduke32-oldmp engine over the 20th Anniversary World Tour on Steam. You still need the original game files, but those shouldn't be too hard to find.If you get it, grab the rtcwcoop 1.0.2 win x64 and RTCWCOOP — Anniversary Upgrade pack for upgraded textures. The Synergy mod for Half-life 2 is really good also, and afaik all of the updated Serious Sam games have co-op modes available.

Portal 2 is the most fun I've had in co-op.

Not exactly FPS but you might enjoy https://store.steampowered.com/app/394510/HELLDIVERS/ Can't see your games owned, so I am not sure if you have played it.
Cheers,
Cruse~

I'm currently playing Borderlands 1 :) I don't have anywhere near that amount of hours but I'm about level 42 on play through one. Beat the game and completed The Zombie Island of Dr. Ned DLC. And did the mission in Mad Moxxi's Underdome Riot. I didn't do the 3 new rooms it opened up though. Not sure if there's another mission or not. But I'm currently doing the Knoxx DLC with a friend and I did start some of the Claptrap's New Robot Revolution DLC already as well. Yeah I know I'm behind a few years :) I beat this for console long ago and didn't really remember it so I figured I would play it again and then go into Borderlands 2.

Borderlands 2 would probably be a great choice since part 1 is so awesome.

How about Dead Island? Played it with a friend and it was pretty fun. Only did the storymode though

I'm surprised no one's mentioned Dying Light yet, unless I missed it somewhere. Fantastic game all around.

Earthfall is ok too with someone else. Dying Light is pretty fun in coop too.

Serious Sam series. They are a lot of fun :)

left 4 dead 2 ? :) . fortnite/ pubg if you care for that battle royale stuff. team fortress 2 / overwatch...warhammer vermintide 1 and/or 2 ... killing floor 1 and/or 2. payday the heist 1 and /or 2. and idk , nothing else comes to mind atm really xd

if you can set it up (through lan, hamachi or whatever) I highly recommend Cry of Fear (free on steam) but the only thing thats funky is that you definitely should play single player first. as the co-op story makes more sense.

fear3 is meh in scariness compared to cry of fear.
although fear3 is more slow n steady kinda scary but still not scary since it became a usual action game.
cry of fear is more pop scarey, although the atmosphere definitely gets at ya too.

FPS:
Payday 2
Killing Floor 1+2
Left 4 Dead 2?
Warhammer Vermintide?

Not First Person but Coop:
Saints Row 3+4+Gat out of Hell
Sniper Elite titles

Not a shooter but First Person:
Portal 2
Dead Island?

Tower Defense FPS:
Sanctum 1+2

Tower Defense Third Person:
Orcs Must Die 2

Not FPS:
Dead Rising titles

Blood and Bacon

Orcs Must Die 2

Call of Duty: World at War ftw!
ARK: Survival Evolved is a good choice (one can host a private server).
Dying Light can be fun too.