My simple brain appreciates simple shooters. Anything beyond moving, shooting, and the occasional secondary weapon makes my think sponge hurt. So I'm glad this game came my way.
With no names or backstories, you're dropped in to kill zombies. Colorful, slow-moving zombies, who pop out of the ground and try to make a meal of you. Killing them nets you experience points to level up different attributes, and ammo and money are found in boxes to aid you in your quest to gun down the undead.
Since the actual gameplay is solid enough, the only thing to complain about is what is the game missing? The one thing I can think of that the game most desperately needed to enhance the gameplay is the option to walk backwards while still firing forward. Without it, you're stuck turning your back to the zombie hoard to get some distance, then quickly turning around to get off a shot or two, then turning away again.
Greater variety in zombie types would've been neat. Aside from the filler slow-walking variety, one explodes in a poison gas, one leaves an acid puddle, and another in riot gear ricochets your bullets back at you. And since they all move more slowly than you, and their numbers are never totally overwhelming, you never get that desperate, fight-to-survive feel that zombie games need to give.
In all, this was a competently made game that fits the zombie-shooter bill nicely. A third game in the series would be welcome, and with a few additions it could be something great.