Just tried the game out.
Here are my specs:
AMD Athlon64 3000+
Here are my impressions:
The game ran fine in both full screen and windowed mode.
It actually ran too fast on my machine. Are you using time-based movement? I got the distinct impression that you weren't because everything just moved too fast. Especially the enemies. Either way, you need to slow down the game.
Now I assume that you were going for a SmashTV sort of feel to the game. Unfortunately, without an analog stick, it's very difficult to play this sort of game. I would recommend adding the ability to use the mouse to aim in ANY direction you want (not just the 8 directions). Playing on a keyboard is just too hard. (Or I just suck which is probably the case.)
The controls are probably my biggest gripe. If a game doesn't control well, I won't play it for very long and herein lies the problems. I played it for about 5 minutes. I got fed up with the controls and uninstalled it. No offense, the game has potential, but without mouse control for aiming, it's just no fun to play.
I hope this helps. Add in mouse control and I'd play it again in a heartbeat because I love SmashTV.