Yeh Dead Island was good fun, played the entire campaign in co-op... It's a bit rinse n repeat, but it holds you. Some of the sections are a bit tiresome too, and the difficulty wavers all over the place. But there's endless loot, some great weapons, a nice ability to play to your style... oh yeah, and a freaking ludicrous and awfully acted storyline... Still, i'm gonna pick up Riptide for the festive season, looks like more of the same with a touch of polish.
Keeping to the zombie thread, Dead Rising II lets you drop in on a friends game... so you can pretty much play the entire campaign co-op too... it's a laugh and well worth a shot.
Tried Resident Evil 5, but it's a bit like playing a PS2 game with slightly nicer gfx... It works, but I got bored pretty fast... My mate is a bigtime RE4 fan tho and managed to deal with its issues and overall enjoyed it.
Dead Space 3 features full campaign co-op... It's pretty much RE4 in space, lovely gfx, pretty intense and relentless... haven't finished it yet, but so far so good.
Farcry 3 is a great game, awesome open world, loads of choices and some crafting... Problem is the 'co-op' is a bunch of shitty linear missions that bare NO resemblance to the game. Avoid for multiplayer at all costs.
Portal 2 is desperately short, but the co-op storyline is just beautiful. Really has you working at it, it's not half as hardcore as the original game... but it's bloody good fun. Tho if one of you loves Portal and the other doesn't get it... I'd skip it, as you just end up sitting there wishing they could see the blindingly obvious.
Inversion - full campaign co-op, but runs badly, shitty gameplay... we made it in a couple sessions then gave up.
Fear 3 has full campaign co-op I'm pretty sure, but haven't gotten around to trying it yet... I had a quick bash at the single player... seems okay, pretty average graphics tho.
Out of the bunch... I'd say I've had the most fun with Dead Island, although it's a game with many many faults... But with a mate on voicechat it becomes pretty good fun... And you gotta love the Michael Jackson dance the 'Thugs' do when they get electrocuted.
mewk