Unpolished
It's playable. Why you'd ever want to past level one, I don't know. This game needs a lot of work on fine tuning. Aura Kits dropped way too often (Wound up having 9 at a time most of the time.) and Rockets (which felt quite necessary to deal with huge crouds) didn't seem to drop at all. Dunno if you have a weight system or not on your rolls, but whatever. Having the idea for upgrades to drop on the fly wasn't exactly the best choice you could have had. It would have been better to have the upgrades occur after each of the too-long waves. The way the firepower upgrade was handled sucked : the damage change wasn't significant, and you're penalized by more of a heat drain? Would have been better if it made your shots hit multiple targets (Ie a cone of bullets?). Coolant sucked - the upgrade didn't really do anything, the regular dump of your heat wasn't enough, and the ten-second drops hardly seemed to drop at all. It really cost way too much to fire your weapon for what its worth. Didn't really notice anything special with self repair or armor kits... but maybe that's just me. Sounds were very repetitive, I hated the voice alert saying "Weapon Overheat" over and over again, was really annoying. Needs music, more sounds for everything, and ambient sounds could help. I found that the tiny bit you scroll between waves of enemies was pointless. Why not just make it automatic? And if you can only move left and right, why even be able to move at all? It's just a turret defense game with legs. The road blocks were annoying, because it took me a minute to realize what the heck was in the way. Found that the helicoptor and jet units were okay, but still quite annoying in swarms because of the whole issue of heat. Kind of wished there was a real plot too, instead of just running around shooting things. I did however like the fact that you can step on enemy units and kill them, but again this brings me back to the whole "left and right" thing.
Overall, the game needs a lot of work to be more than average. It's a good start, and with a bit of reworking it might be great.
Oh and hey, get rid of the concept of lives in that game, there's no reason to be dying at all unless you're just terrible.