The thing that makes me like gemcraft more than other tower defence games is the fact that I can level everything evenly, i can create higher level attacks without much difficulty, and i do not have to wait for anything other than mana to upgrade. Keep it up :)
Graphics are a little dull, scrolling is annoying. I'd like the minimap to scroll smoothly when I am moving it. Could use more tank styles. Shooting off a bridge at enemy shot water, even when aimed directly at enemy. Maybe could use a way to choose the path for your tank to move to that spot instead of random path. My tanks were stupid but powerful. Different difficulties.. Much more..