Generally, a very good game, though the hard and insane modes are very disappointing, as they consist mainly of replaying the same bosses with a faster time constant, rescaled damage, and more expensive items (that generally do the same thing). This game doesn't really feel like the effort was placed in it that can be found in other popular NG bullet hells.
As another example, the bullet patterns of these bosses employ massive amounts of randomness, where more serious bullet hells have very carefully calculated bullet patterns. Of course, this doesn't really matter much until Insane mode, where most bosses can kill you in 2 hits. Generally, as a game design principle, randomness and lack-of-forgiveness don't go together. In easier modes, the randomness can be forgiven with the inbuilt healing systems and bosses' low damage output, but this terrible combination makes some bosses of the Insane mode inordinately dependent on luck. (Some of them, I cleared first try without actually trying, like boss 8, and others took many many tries, like boss 6, or 10)
I should mention that the walls boss 6 makes are an interesting touch, but due to the randomness re: earlier, he has a relatively high chance of sending a bullet right toward the opening of the wall, creating a damned-if-you-do/damned-if-you-don't situation.
I also want to point out that the cyclops boss (boss 9) is wonderful, but there seems to be a bug - after he leans down to the table: the first fist slam after he stands back up will not actually be connected to his arm, fixing itself for the remaining fist slams.
As far as item balancing goes: although I can understand you probably did this to make calibrating the boss health easier, the huge nerf of additional bullets from your last game makes items that do little other than increase bullet count not worth wasting the item slot on unless your damage is extraordinarily high. I would suggest that the nerf is probably excessive. Remember that serious players (like myself) will actually do the math to see what item combinations have the most impact on damage output.
Finally, in games like this, it is usually a nice touch to allow players to skip straight to hard mode - it helps the game experience, as being forced to go though easier modes feels very much like grinding (especially in games like this that introduce nothing new when replaying older bosses). I would also request that insane mode changed some aspect of the bosses (they had new moves, different patterns, etc), as opposed to just being 'faster'.
All in all, the game was most enjoyable to play on hard mode - I personally had a blast. Unfortunately, there are too many other flaws to this game to take it seriously, or to give it replay value (which is compounded by the game forcing you 'replay' it 3 times just in the course of playing it once).
Hopefully some of the above was helpful. Looking forward to a more polished installment when you make the third! ^^