After Some Multi-Player CoOp Game Recommendations

Hmm, looking through my library...I think most if not all of these are 4 players.

Borderlands 2 is a great co-op game with a lot of albeit cheesy humor
Battleblock Theatre is another goofy side scoller with co-op and versus modes
Magicka is an overhead action fantasy game, pretty funny too. Could potentially ruin friendships though.
Payday 2 is a great co-op heist game with some humor. Don't like what they've done with the DLC, but you can ignore all that.

Terraria / Starbound - 2d crafting / survival platform games. A lot of fun if you like building, open world type stuff.
Far Cry 3 has some nice co-op missions
Grim Dawn is a fun ARPG from the creators of Titan Quest, if you like Diablo style games (
The new Gauntlet is a nice reboot of the classic
Left 4 Dead 2 - need I mention this one? Co-op zombie killin' FPS.

These are pvp but can be really casual, joking around games:
Golf With Your Friends
Basically any Worms game (can play with one copy or each on own computer)

If you each have a phone/tablet you could use (only need 1 copy of the game): The Jackbox Party Pack

If you each have xbox controllers...only Overcooked NEEDS controllers but the other 2 games are recommended playing with controllers if possible (these aren't pvp):
Battleblock Theater
Castle Crashers
Overcooked (only one person needs to have the game)

Those mentioned above and i would recommend Serious Sam 3 BFE i played a 12 player co/op one and its a blast +p
Team fortress 2
If u switch between numbers than maybe Rampage Knights 2player

Magicka is sooo fun, also Dungeon Defenders (the second one is f2p) Portal 2 its fun too, but its only for 2 players

Most MMORPG games are co-oplike, the most recent one I have done with some pals is Path of Exile.

But the best co-op game (besides L4D2 which is mentioned above me) I can imagine is Battleblock Theater, which is a very silly and hilarious platformer for 2 players (sadly not more).

You could of course also play an oldschool arcade game and take turns upon dying or finishing a level, because that never gets boring.

Lovers in a Dangerous Spacetime
http://store.steampowered.com/app/252110/

Broforce
http://store.steampowered.com/app/274190/

Dangerous Golf
http://store.steampowered.com/app/405500/

list of co-op games that belong to my favorite group, tower defense meets fps
Sanctum http://store.steampowered.com/app/91600/
Sanctum 2 http://store.steampowered.com/app/210770/
dungeon defenders http://store.steampowered.com/app/65800/
dungeon defenders 2 http://store.steampowered.com/app/236110/

coop games of other genres
Rocket League http://store.steampowered.com/app/252950/ (football with cars)
Portal 2 (2 player coop) http://store.steampowered.com/app/620 (puzzle game)
Trine (1, 2 and 3) http://store.steampowered.com/app/35700 (platformer, side scroller)
Torchlight II http://store.steampowered.com/app/200710/ (rpg)
It came from space and ate our brain http://store.steampowered.com/app/342620/ (indie)

Borderlands series, Dead by Daylight, L4D2, Rust, Killing Floor 1, 2

Dying light is awesooome!)