I found this to be an incredibly cool game! I think the biggest reason it works is how simple it is. It's just another standard stick game where you destroy everything in sight. I don't know if the different colored enemies have different kinds of health. It's just wonderful to play.
A pity the tank can't jump. Of course, it's pretty much unstoppable as enemies are just killed by being around it! In general, they're not that easy to kill, because they're so many of them. I love the screams they make as they die. It's just all around fun!