Having a consistent art design is fine, but a lot of the visuals just blend together too much. My shots looks like enemy shots, money and bombs blend into the random stars... It's just a lot of visual chaos I think could be toned down.
Okay, 1 problem with endless mode is that the rewards are based on the boss, not the difficulty or duration. Boss 5 might be the beetle, but still getting minimal rewards when it's got ramped up health like that seems terrible to play against.
This game is really good, it just feels like it's missing something somewhere. I can't quite put my finger on it. (Badges would be really good though.)
I feel like the money-to-progression ratio is a hair off. And I have to agree with the point on the enemy bullets feel like they need to be more visible.
Nice game overall, but it does feel like the screen is too busy. It's difficult to play without needing to pause and unpause constantly to check back and forth between things.
Oh yeah. And as usual, follow the "Like Us" links for 400$ a piece (4 of them). You can close the window/tab before it loads and it still gives you the money. Free early upgrades are good.