Dead Nation has some great zombie action, but a bit more depth in content wouldn't hurt.
Environments are diverse, ranging from city streets to parks, graveyards, hospitals, roofs and more. All of them are strictly exteriors, not even once will you find yourself inside any type of building. Most of them appear to be fairly linear and will make you run in the direction of the next checkpoint. Not even once will you have to backtrack to a previously visited location to use any kind of key item. You will encounter many types of zombies, from regular citizens to cops, firemen, soldiers, businessmen and some special bigger types.
Some of the weapons at your disposal are rifles, shotguns, sub machine guns, rocket launchers, flamethrowers, grenades, mines, molotov cocktails, dynamite and a few more. Each of those can be upgraded at a checkpoint using loot you have obtained by either killing zombies or searching cars and containers.
There are a few ways you can distract a horde of zombies, by throwing flares to get their attention, by shooting cars to activate their alarms, or by shooting vending machines to spill out cans of beverage. Cars can also explode after some abuse and they are a cheap way to take out a bunch of zombies, just be sure to loot it for cash beforehand.
In some of the containers you can find additional armor pieces, which can improve various stats and make you perform differently in action. Dead Nation offers a lot of diverse ways to battle the undead, but there is one thing Dead Nation fails to deliver, and that is diversity in objectives.
While you will be given a task to perform in the cinematics that take place between levels and are presented in voiced over still images, when playing the game you will have only one objective, and that is reaching the next checkpoint regardless of what you should be doing plot wise.
Dead Nation can be played with a friend, and it definitely gets more fun as there are even more zombies to have fun with, just don't get to excited about playing with strangers as there either doesn't seem to be a way to search for online games, or only send out invites to the people in your list. Another thing to note is the lack of voice chat, but apparently the next update should take care of that.
If you want to kill a ton of zombies and have fun doing it, then Dead Nation is just the right game for you, but if you want a more deeper plot driven experience then think twice before considering this.