Great! It just needs a few tweaks.
Not bad. Not bad at all. I loved how the upgrades are actually useful unlike a lot of other defense games. The final boss was also a nice touch. It actually makes you think instead of abusing your speed and strength upgrades. The combo of enemies in the swarm stages helped keep things lively, though some of the later swarm stages seemed unnecessary. One problem I had though was that nothing happened after I ran the final boss out of HP. Another issue was the lack of an indicator when you max out an upgrade, or how much more of the upgrade you can get.