But not so good either. The exp thing was bugged, so it never ran out once you got it. I didnt mind that, becuase it allowd me to get the upgraded weapons, which were the only thing that saved my ass a lot of times.
I found i could play through the entire game with only 3 freeze towers, and 5 cannon towers, and just upgrade to cannon towers after that. As long asw you place them strategically. The wave and sniper towers were amazing at higher levels, but cost so much to upgrade, that you couldnt get the final upgrade untill the last few waves. which meant the rest of your defence was suffering becuase you wernt spending any money on other towers.
For those of you having a hard time with this game, get the shield. It should reduce damage from 150, down to 17 or so. time it right, and you can defend against anything that gets through.
Anyway, good game, but the difficulty does ramp up a bit quickly. Overall, once i fugred out my towers, it was rather easy though.