Umm...
It's "OK" and that's about it. The game is horribly balanced to the point where you don't need troops or even your castle's defenses. Just a small handful of red towers to get you started, some upgrades to their speed, and then almost straight to black towers to make the game even more boring. I've gone through 100 waves now without making a single mouseclic..not to upgrade anything, not to build anything new..nothing. I've just let the game run in the background and it's STILL going. The A.I. for the enemies is nonexistant. The A.I. for your own troops is pitiful at best. It's a good START to a game but there's no reason to even bother playing to wave 30 where you get the pretty blue ribbon because by the time you've passed wave 10 you can almost quit playing altogether and still succeed.
Perhaps more variety of towers, more variety of upgrades, more than the same 20 second soundtrack over and over and over...as it is though...bleh.