This is an original concept, and I do very much enjoy it. There are a large fistful of things that stops this from being a high-calibur product though, in my eyes. I'll list some bulletins, and I'm sure some people will agree with them and some people won't.
-Powerups and health don't last very long in the air. Additionally, many kinds of exploding munitions or minions seem to have the explosive effect make the powerup invisible until its last split second of lifetime.
-Many of the powerup weapons are ill-explained and TERRIBLY balanced. I am aware that some powerups seem to be rarer than others and some enter the game later on, which should make them more powerful. The being said, the flintlock looking pistol was useless, the scattershot weapon was so puny you can hover next to minions shooting them point blank and the puny minion won't even die. The charge up laser was pretty awful IMO. The sound was loud and high-pitched, making it annoying. It's fire rate was very low, its stopping power equally minimal, and its multi-penetration ability sometimes failed for unknown reasons. Additionally, the rocket launcher was alright earlier game but got tedious and the iron fist is outrageously overpowered, but on the plus side it does keep me grabbing for powerups in an attempt to get one.
-Powerups have no way of indicating their ammunition or how long they last, which is somewhat counter productive.
-The music, while nice and cinematic, didn't seem quite suited for the action scenes and really got annoying in addition to not getting the blood pumping. Seeing how this is bullet hell-like in gameplay, lots of gamers are probably looking for an energy-filled soundtrack they can get into while shredding their foes in a hardcore battle to the death.
-Hats were really, really cheap and their effects weren't really clear in magnitude as well as some of them being uniquely present to the hats family and not shared in upgrades. This really leaves the player unsure what "+2 health and +16 money" does in its full magnitude.
-Although there was definitely a large variety of parts later on, the total pool of enemy variety does feel stale at some points, and especially after playing through 40 or so bosses. I'm sure you're already hard-pressed to find lots of original ideas for parts, so I'm not really counting this one against you. This unique game has that at the center of its concern.
-Dialogue at beginning of fights would've been something I'd prefer an option to skip. Maybe there is one but if so I haven't found it.
I don't want to seem like a dick or just sit here and bag on this game. My underlying opinion of this game is rather positive because it is new and fresh and experimental. However, these aspects also provide lots of new areas that could seem worth polishing or developing, and I hope this feedback helps or at least gets the gears turning for the next project you ensue, though I'm sure other people (more and less literately than myself) have pointed out a number of these points previously.
This is a solid product, but is still not in the "wow" zone for entertainment. I applaud the unique ideas and new concepts being employed.
7/10, 3/5 (borderline decision, sorry. I just sat back and sighed in my chair contemplating this one pretty hard) ~WCCC