whichever the one my internet can handle without lag.

Bomberman! (Seriously, it's amazing. Get a few friends together (everyone needs a controller), have something to drink at hand, and laugh the night away).

But more seriously, we don't know what you like. I might say that I think that Europa Universalis 4 is great in multiplayer (I really think it is), but I don't know if you like that type of games.

Brawlhalla is quite fun.

borderlands2

imho is Payday 2 one of the best coop games :)

Dead Space 3
Lara Croft and the Guardian of Light

borderlands 2, dying light

Duck Game is amazing. It may not look like much on the surface, but the quick rounds, tight controls, and massive selection of weaponry makes it like a real-time version of Worms. Only problem is, it's a bit expensive for what it is. I've been hoping to see some giveaways of it on here, but it doesn't seem to be a very popular choice. :(

Best multiplayer. I think Counter-Strike : Global Offensive
Good co-ops : Borderlands 2,Borderlands The Pre-Sequel, Left 4 Dead 2

noone said magicka already? best "coop" ever

All depends on what are in mood for:

1. Playing together even if you can beat game solo: Trine
2. Show how good and close team you are.. pretty much any FPS type, I'm guessing Payday
3. Have blast blasting each other: Magicka, maybe even Borderlands
4. Ruin friendship for all time: any MOBA

If you want something funny try Bomberman as said in comment above , but if you want a game to complete it with one friend you should play Diablo 1 because it's so awesome

DAMNED

Speedrunners!!

• dead island saga
• borderland saga
• minecraft
• terraria
• starbound
• ark : survival evolved (though i could only see video of it)
• saints row 3
• payday 2
• magicka 1 & 2
• serious sam saga
• left 4 dead saga (though i am not a big fan myself)
• dark souls

these are the only i can think on PC right now.
Also, you can check some mmo, with friends some can be quite fun, i liked doing the secret world in duo (I think this game would have been even greater if it was made for solo or little group of people than a mmo :p)

which of COD series have coop 4 man ?
zombie or coop compaing