Help me choose an easy and simple Coop game from my library (or not) [GA inside]

Try Worms Ultimate Mayhem. U can buy 1 copy and play on the same computer up to 4 players. Its a funny turn based game, its also 3D unlike the others in the series. Or u can play the story and take turns controlling the 4 worms that u can customise(maybe 2 worms for each of u?). Its a quick easy game. should give it a shot. http://store.steampowered.com/app/70600/?l=french

EDIT: U already own this game as well.
P.s U have waay too many games lol.

I have absolutely no idea how nobody recommended this
http://www.lorenzostanco.com/lab/steam/

I use it everytime me and my gf want to find something to play.

1. Enter your steam ID
2. Sort by: Metascore
3. Filter by features: Co-op

My votes go to
Terraria ( if you have LOTS of time. You will love it. )
Portal 2
Borderlands
Audiosurf

You have many good ones. Maybe watch some of their trailers together.

Chariot is a little coop gem, my GF isn't a gamer and really enjoyed it

Buy Nintendo Wii, you won't regret !

Not entirely what you're looking for, but I started playing Scribblenauts with my gaming-novice fiancee and she LOVED it. I controlled Max and did all the movement since she doesn't have any digital coordination, but she had first crack at solving the puzzles. Sometimes she was allowed to pick the noun and I picked the adjective, and that way i was able to either help a puzzle if I could figure it out and she couldn't, or I could just be ridiculous and silly about it.

Just throwing some stuff out there.

Duke Nukem 3D: Megaton Edition
Dungeon Siege/Dungeon Siege 2
Lara Croft and the Guardian of Light
ibb & obb
Terraria

Free to play:
Path of Exile
Warframe
Robocraft
TERA
Dungeon Defenders II

i would for one go way less towards what you consider difficult and go more like what kind of game she finds interesting. if one likes a genre the learning curve is in general much easier :)

personally i think Borderlands is insanely fun and something one can try easily because its so often on sale. played it with lots of ppl now and alone just driving through the game is so much fun.

my boyfriend wants to try out Monacco with me do that may be fun too.

Game I dont rec is White Noise. Played it with a friend and for short and gimmicky it was okay. But it mostly frustrated us which made me sad. i had been looking forward to it.

Gears of War?

My best are already listed due to being late to the party, but hopefully this bump will help someone else notice this and give you a good suggestion.