I'm mostly playing Gears of War Judgment and a bit of R.e. 5 and 6 mercenaries on the side.
I really enjoy Dead Island, i have both the new ones called Riptide. Their fantastic games, one of the best 'long' zombie games, kind of an RPG in the style of fallout but more simpler in terms of characters and quests. There are many subquests and you can do a new game + with all your items carried over. the zombies in dead island are some of the best video game zombies ever, you have walkers (shuffling romero classics), infected (28 days later runners), and a variety of specials. Its hard and loads of fun in co op.
Gears Judgment is my favourite game for straight versus online battling, i play domination with a team and we have a laugh most days on that.
Im looking forward big time to State of Decay, a part sim part action survival zombie apocalypse game, third person, where you control a group of survivors and make a base to survive, with the game carrying on when you log out. It willl be about 1200 points on xbox live arcade coming out in June, suggest you check that out!