The game itself is by the same company that made Super Stardust HD, so that was enough reason alone for me to give the game a shot. It's a co-op, top down shooter. Basically like a top down L4D. The graphics are great, with an amazing amount of zombies on screen at once. It's fast paced and can get really frantic at times.
However!
The game is waaaay too dark and there is no way to up the gamma in-game. It can get really frustrating at times due to this single issue. Also, the default weapon is a single shot rifle, so you have to push the bumper every single goddamn time to fire. In a fast and frantic twin stick shooter, you'll be doing that A LOT. As in, thousands and thousands of times. There are other weapons, but your rifle is the only one with unlimited ammo, so it is easily your mainstay. The other thing is that save points are few and far between. I played for about an hour but had to leave, so instead of pausing and leaving my PS3 on, I opted to shut it off and lose all my progress instead

At least you have to use more strategy than usual for this type of game. I also enjoy the upgrade options for both weapons and armor. Nice additions.
Zombie Apocalypse, although vastly inferior in terms of graphics and overall package, it's still more fun for what it is trying to do. Dead Nation is trying to take the "arena shooter" to the next level, but the little issues end up holding it back a great deal IMO. Alien Swarm is free in Steam and basically does what Dead Nation is trying to do a heck of a lot better (and it's free). If Housemarque would fix just a couple of nagging issues, this would be easy to recommend.