Back to 2009 I bought and played Torchlight, a quite brilliant hack n slash / action RPG video game for PC. I had a lot of fun and the only flaw the game suffered was the lack of a multiplayer.
But this year, Runic Games, the developer of the game released its sequel with a brilliant multiplayer. I have been able to play in cooperation with a good friend of mine and I daresay it was pretty good fun.
A coop mode should be present in many more games as they are nowadays. I really had a lot of fun playing Portal 2 in coop and Torchlight proves to be as much fun.
Now the only thing I can say against this brilliant game is that I had approximately one computer crash for every hour I played this game online with my friend. Quite a big problem but since the game was a whole lot of fun and that I paid less than ten euros for it thanks to the Steam sales, I am not really complaining.