Dead Island is an upcoming open world horror action adventure video game in development by Techland for Microsoft Windows, Playstation 3 and Xbox 360. It is centered on the challenge of survival on a zombie-infested island with a major emphasis on melee combat.
So, as it says there, it's open world. And it's going to be co-op.
This game really looks like FarCry 2 mixed with L4D mixed with Dead Rising.
Video:
http://www.youtube.com/watch?v=UDzFzNg0bxkScreenshots:



It's believed to be released August 1st, and the video is still a video of the beta so don't complain.
There will be guns, but as he said in the video, they will be in very short supply and have hardly any ammo, so you're gonna have to use what you can.