It's a timeless tale - boy-fish meets girl-fish; girl-fish is killed by some scientist; boy-fish is experimented on; boy-fish is dumped and eaten by other fish; boy-fish becomes zombie fish. As a zombie fish you are swimming around different environments eating smaller fish until you eat enough to become larger. Then you eat bigger fish until you get to a boss and move on to the next environment. For the majority of the game you are repeating the same thing with increasing difficulty, although there are stages where you are pushed forward and the only goal is to survive. Unfortunately it does not last long.
There is also a fish tank which you can purchase fish and decorations for. The tank doesn't serve much purpose except to store stat boosting fish in, such as improving your speed, armour, etc. but you are limited in the number you can have and need to choose an appropriate mix.
There are plenty of different environments to see but for the most part they are just different dingy, grimy areas. The fish are cartoony and kind of gross, and there are a variety of different fish to see, eat or avoid. When the playing area is full of fish it makes seeing power ups/power downs difficult to distinguish, and you can quickly find yourself poisoned and floating exposed in the path of larger fish.
The music is what you'd expect from a zombie themed game - creepy.
Zombie fish is controlled by tilting the phone to move him around the play area. How much you like the controls comes down to how much you like tilt-based games. Over time, the calibration of the tilt messes up. You can change over to a virtual joystick but it only makes it harder to play.
What In-app Purchases are there?
You can either earn or purchase 'zomboils' in the game to unlock one-off powerups, upgrades or buy fish that offer extra stats to chuck in your fish tank which you can also decorate.
Zombie Fish Tank is a competent game and there's plenty of levels and a story running through it, it's just unfortunate that the gameplay never changes that much. If you enjoy tilt-based games with a creepy zombie vibe you'll be able to sink a few hours into this game completing goals and building upon your fish tank. To get the most out of this game I recommend playing in bite sized chunks to keep it fresh.
A word of warning though for those that value their iPhone/iPod/iPad storage. The game says the download is 248mb, but space this game expands out to hit nearly 1 gig, so make sure to keep plenty of space for the install.