When I first read the description I wondered why there weren't upgrades. After playing I understand that this game was not meant for upgrades, nor should they be implemented. This is a true "arcade" style game. The only replay value is in trying to beat your high score. Of course, the actual game was somewhat lacking. It seems to be inspired by Geometry Wars (grided background, lots of neon), however the game doesn't really compare. I imagine that the health bar was something you thought of to make this game different and avoid being a clone of Geometry Wars. However... in my opinion it really slowed the game down. In Geometry Wars, the one collision one life method really works well. It makes the game a truly frantic test of skill. This game tries too hard to transition difficulty, it starts at a crawl and doesn't really get hectic till round 15 or so. I don't know if you intend to update this, but if you do I would advise eliminating the first 10 or so rounds entirely. To go back to the health bar... the amount of health is way too high. I died more because I stopped caring than because of the pidley damage caused by running into things. Considering the size of the health bar, the health packs just break the game. I survived 3 or 4 more rounds than I should have after the apathy set in because of them. I think I understand that you were trying to put a unique spin on this genre of game. I appreciate that there are still people being innovative, however you have to watch out that you leave the core experience in tact. The game is far too slow and far too easy. It just doesn't have that strangely delightful stress, that stupidly frantic game play, the tension, pretty much all the key points in this style of game. I realize that this review is getting really long, so I'll just give you advice on how to make the game better
1. The number of enemies who actually go after the player is too small.
2. The enemies aren't very unique. You would be better off with six or seven unique enemies than 13 generic ones. The biggest differences were health and size, and some did chase you, but most kinda just floated around. You should give the enemies unique behavior, movements and appearances.
3. Nerf the health. The point in this game is to score, not survive. If the game timer is to be believed it took me 16 minutes to die on my first attempt. I think the first 10 minutes were just a waste of time. Put some kind of combo or score multiplier in for replayability. As it is now, score is more of a function of the time spent playing than skill.
4. You might want to put some enemies that actually shoot back. If you don't die on contact and don't get completely mobbed by enemies you need to make them shoot back. Give me something to dodge.
I apologize for the length, but I think you could really improve this game even after release.