What are some fun co-op games?

[I AM THE LAW]

It doesn't need to have a good story, just if it's game play is fun. Thanks.

[Dr.Critic]

Rainbow 6 Vegas 2. Cheap as chips, lots of progression and changing gameplay, teamwork required so long as you play on realistic and very challenging, yet very fun.

Dawn of War 2 Retribution has a pretty good coop campaign, and its nowhere near as boring in coop as with the first two titles in that series.

Saints Row III or possibly IV, though I haven't played the latter are pretty fun in coop. Over the top gameplay, fairly hilarious too.

Arma 2 or 3 are very, very fun coop games but only if you know what you're doing. You can create just about any type of mission or download any type of mission and have a lot of fun with it; I whipped up a dogfighting mission with a two-seater F14 that me and my friend piloted a while ago:

[t]http://cloud-3.steampowered.com/ugc/651002589717730228/FEF98212DDFF42FE09FF34D316F07B64ECA9FB33/1024x768.resizedimage[/t]

Shit was mental.

[Kirbyfactor]

Castle crashers
Magicka
Battleblock theatre

[Zonesylvania]

broforce

[TheNickle]

Timesplitter series?
2 and future perfect especially.

[WishesForFishes]

I'll say it a third time
[img]http://www.gizorama.com/wp-content/uploads/2013/03/a.jpg[/img]

[editline]29th June 2014[/editline]

[QUOTE=Zonesylvania;45243900]broforce[/QUOTE]

Shit, that's co-op?

[Infab]

DOOM series

[Bradyns]

Splinter Cell: Chaos Theory.

[kill3r]

[QUOTE=Bradyns;45296269]Splinter Cell: Chaos Theory.[/QUOTE]

And blacklist too

PAYDAY 2

[Bad Joe]

serious sam

[Deleted1912]

Metal Slug 3

[Viomi]

Borderlands
Don't Starve (Soon to have Multiplayer)
System Shock 2
Trine 2
Sanctum & Sanctum 2
Portal 2
Nation Red
Magicka
Left 4 Dead & Left 4 Dead 2
How to Survive
Guns of Icarus Online
FEAR 3
Dungeon Defenders
Project Zomboid
DayZ
Rust
Terraria
Minecraft
Dead Space 3
Damned
Saints Row IV & Saints Row: The Third

[slashsnemesis]

[URL="http://facepunch.com/showthread.php?t=1406182"]Due Process[/URL]

[RustledJimmys]

Halo 3 Legendary

[SpeedyHeart]

Payday the heist

[Cabbage]

[QUOTE=RustledJimmys;45299140]Halo 3 Legendary[/QUOTE]

god damn playing co-op Halo 3+Reach LASO was so infuriating but so fun and requires an insane amount of teamwork

pretty sure it's impossible solo

[Merlina]

Kayne and Lynch: 2 Dog Days

[ThreeFour]

Ontop the previous splintercell suggestions, We can also mention Conviction.
Rainbow Six 3 : Raven Shield
AI War : Fleet command
Magicite
Killing floor.

[Echidna666]

Forced is fun

[UntouchedShadow]

Viscera Cleanup Detail is hilariously fun to play with friends, especially when you discover the Microsoft Sam text to speech function.

[Zannabluke]

killing floor

[KIDzilla]

Lost Planet 2