Recommend a good co-op game for new gamer and onboard graphics?

[Hallowsend]

I am looking for some good co-op games to play with my girlfriend, who only has laptops with onboard graphics. That rules out most newer FPSs with co-op (Portal 2, etc) and she is new-ish to video games, so best to keep them uncomplicated.

We have been having fun with Hammerwatch but I wonder if there are any other good co-op games others might recommend too.

Requirements are:
Co-op campaign
Internet co-op
Suitable for onboard graphics (platformers only?)
Reasonably straightforward (not complex RTSs)

Thanks for any suggestions!

[WhiteKnight77]

Ghost Recon with Desert Siege and Island Thunder. There are hundreds of mods for it too that take up at last count, 7 DVDs.

[grounded in reality]

king Arthur's gold
it's not gpu intensive

http://youtu.be/d6Eom7IGLRw

[enamel]

Not on Steam, but Minecraft is one of the best co-op games of all time in my opinion.

[Hallowsend]

Ghost Recons could be a hoot but I think may not be so girlfriend-friendly.
People seem to rave about KAG - I'll check it out but it would be good to play a campaigney kind of game. I know Minecraft is good fun too but we're hoping to play through a story rather than pure MP action.

[Hallowsend]

Games like Trine 2 maybe?