First of all, nice little blast from the past on the first level. They enemies pulled right of Tyrian took me way back. Second of all, your upgrade screen sucks. Third of all, the insta-kill second boss made me want to personally harm you, and quit the game. I did one of these.
While the game is fun, it gets repetitive very quickly and has little replay value. I agree that a more branched upgrade tree would make it better, as well as perhaps a story and perhaps the ability to control units as groups or set rally points to keep the clicking down.
I will admit that this is excellent for a Flash RTS, but with nothing special to set it apart from being just another Command and Conquer clone, it gets old fast.
Not really a bad game, just not that much gameplay. No change in scenery or enemies, and very limited upgrades. Also, not sure if it's a bug but the final weapon doesn't give you money for kills.
Game would be more fun with upgrades, levels, etc. All been said before. Also, there's a glitch that makes the cannon fire continuous charged shots. Don't know how it happened.