Woohoo!
Ah man I've been playing this game like for the last 2 hours x'D
Got rank 31 on the highscore list so I can't deny it's a fun game :)
However:
*As PRZ18 pointed out;
Auto is useless, bashing the button while in single mode is much faster and doesn't drain ammo (which means you can bashbashbash switch to shotgun shoot a few times and go back to single and do way more DPS)
*Some upgrades aren't balanced e.g. the ships manual cannon packed a punch in the first rounds but afterwards was a wasted investment because it's stationary, ammodrainer, takes time to use; all in all the gun was a much better choice in combination with the grenade
*Upgrades don't affect the weapons visuals which is a shame because I'm pretty sure that it wouldn't take much trouble to program that in
*Every round you get more monsters and that every round they get a bit harder however you always get the same amount of energy for certain types of monsters meaning that the amount of energy per round increases linear and the difficulty lvl increases quadratic.. which means sooner or later you've got a problem even before maxing out 1 or 2 weapons
Don't get me wrong, I'm giving you critique because I like the game and because I believe you can make it even more awesome :)