My personnal top eleven of indie coop games

Spelunky

++ : Highly addictive. A really graduating feeling of progession. Lots of secrets. Perfect soundtrack. Kiss from a pug included.
-- : It is so hard not to kill each other when throwing a stone at a spider.

http://store.steampowered.com/app/239350/
Original version : http://spelunkyworld.com/original.html

Battleblock Theater

++ : Great sense of humour, really challenging, cute cats. I said : cute cats.
-- : A bit too short.

http://store.steampowered.com/app/238460/

Don't Starve Together

++ : Best survival game imo, absolutely time-consuming.
-- : The most punitive game I ever played.

http://store.steampowered.com/app/322330/

Guacamelee

++ : Very nice artistic direction ! Original, enjoyable and fluid.
-- : Bit too short also. But that's the only con I can think of.

http://store.steampowered.com/app/214770/

Nuclear Throne

++ : Many possibilities, much frustration, nice rewards !
-- : Ended up playing with the same characters over and over.

http://store.steampowered.com/app/242680/

Gauntlet

++ : Co-op also online. Good difficulty progession. Classic.
-- : Only two characters are really interesting when upgraded. Arcade mode presents not much interest.

http://store.steampowered.com/app/258970/

Enter the Gungeon

++ : Fun, with secrets rooms and guns absolutely everywhere.
-- : Many guns but not that many ways of shooting, sad.

http://store.steampowered.com/app/311690/

Towerfall

++ : Friendly fire, punchy, and addictive.
-- : Not enough levels (but more recently added).

http://store.steampowered.com/app/251470/

Dead Nation

++ : Zombies everywhere ! True co-op and moments of real tension.
-- : Not enough differents guns (you'll be hearing that woman's voice in your head for a long time).

http://www.housemarque.com/games/dead-nation/

BroForce

++ : Lots of references, bloody good time, feeling like a true hardcore hero when a mission is completed (that guitar solo...!).
-- : Characters quickly unlocked. Not enough missions.

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

Binding of Isaac Rebirth

++ : Every benefits of the original without having to wait your turn.
-- : Not exactly a co-op game... more a way of helping/ getting your partner killed.

http://store.steampowered.com/agecheck/app/250900/

Cats tax