One of the things I miss about video games is the fact that you used to be able to throw a cartridge into something, boot it up, and play it for about 10 minutes and make some actual progress or have a little bit of fun on the way. Truly, a few video games of the past really fit this bill perfectly as little time wasters. This is one of those games, though after having a couple of hours of play invested in it, I do feel the need to point out some problems that I haven't seen other reviews point out.
The idea of shooting zombies is one that has been done one million times, now this isn't necessarily a drawback, but it seems a lot more like some of the characters in this game are mutants rather than zombies. Zombies are a pretty straightforward concept, and though I do like some variation in the type of zombies, there's usually an archetype that people tend to expect when shooting at them.
In other words, zombies coming at you with rocket launchers and guns doesn't make much sense. However, this is balanced by the fact that there are zombie dogs and zombie rats, which I always find entertaining.
Another thing that I will give this game credit for is that it definitely fits its name, it is Zombie Shooter, and you will not play another Zombie Shooter that is quite as Zombie or quite as Shootie as this one. Well, you probably will, you probably have! As others have said, there's no really new ground covered here, but that's not necessarily a bad thing. If you're looking for a game that you can roll out of bed and play for a few minutes then turn off without feeling guilty about the amount of progress you've made because you just needed something to play while you wake up and drink your coffee, this may help you metabolize that caffeine a little easier.
Now I will move on to some improvements that I feel would make this game better and more enjoyable. First of all, fix it so you can move around certain dead zombies - you will get stuck at times and have to completely exit to the Main menu and restart the level because you get stuck behind them and cannot escape. This also happens with extras boxes, certain walls, you name it. Sometimes, you just get stuck, and you can't get out of that position. This is irritating, even if you're simply playing for ten minutes. If you get super involved with it and decide to play for more than a half hour (or as long as you can take hearing "BLARGH ARGH THUMPTHUMP WHOMP BLLAAAHHHGHHGHHRHRHARRGHHURGLE" and get stuck behind something, you will have a screaming fit with your monitor. At least you will if you're as impatient as I am. In other words: Patch this. Just make it so you can walk over all dead zombie types, you can walk over most of them as they vaporize into a puddle of red goop, why not all of them? Yes, your character designs for the ones that mutate or shoot several tongues at you are awesome, but when they're dead you don't need to make them immovable objects.
Second, fix the night vision. The night vision sucks. It's easier to see without it in 99% of cases.
Maybe have different types of drones. I realize that the drone is a little bit of a wuss move for anyone to make playing this game, but having the option definitely helps, but the one drone option that is available is surprisingly useful..for about 30 seconds, before it gets blown up by a zombie lobbing rockets at you (again, this doesn't make sense in a zombie game, but I'm not looking for realism in something like this.)
Fourth, maybe throw some steam achievements or trading cards in there. I don't know how much effort this takes on the part of the publisher or whoever programs the game, and I know many would argue that it ruins the fun of playing because it takes the focus away from the gameplay and more toward the achievements, but come on, achievements are cool! It's not that they replace real life achievements such as learning to play the guitar or landing a promotion at your job, it's that they're neat little decorations for your profile, or bragging rights whenever one of your friends insists they've gotten further in a game than you have. "Oh yeah?!" you will say, and show them the achievement that proves otherwise, that you splattered more idiot rocket-launcher wielding zombies than they did, that you survived an onslaught of 8,000 mindless "GUUUHHHRRGHHHS" coming at your face while trying to turn the lights on in another underground vault for the 900th time.
I'm going to wrap this up by saying that this game is worth the money depending on what you want to get out of it. I don't think anyone reading this review or buying the game is expecting a AAA title or to invest a hundred hours of their time into it, but it is worth the money to play it and I would recommend it, just be prepared for some somewhat irritating moments when you get stuck behind something that has the health that you desperately need and you have to completely restart the level because of this. Also be prepared to become quickly annoyed with having zombies shoot rockets at you without actually attempting to eat your brain. Finally, one thing I didn't mention in this review that bears mentioning is that the RPG elements are extremely fun. They do have real impact to your gameplay, and playing with them does make you consider whether or not you're making the best use of the game money you spent to get through each level.
So whether you're looking to waste some time or....waste some time, pick this up. When I weigh the problems of this game with the positives of it, I have to give it a 6.5 out of 10. With a patch, it could easily be taken up to 7.5. Good job, guys.