I liked it a lot!
The drain may be a bit unbalanced, but apart from that the concept is really creative: the higher the damage done, the higher the risk.
It's a nice change from the random aspect of dice, since here we're in full control, and it makes juggling with power a nice strategic aspect.
Visually, it's simple, but in a good way. The sound effects are cool too.
Great submission, and excellent work for a first game! =)