I love this game. I played through it twice. I like the depth and the freedom to do things in any order. The music is good too, if a bit repetitive. Some tracks reminded me of the music style of StarCraft 1.
The bosses could have been a bit more interesting though imho. Most bosses don't really require a lot of strategy, they just float there doing nothing, most don't shoot anything, and those that do are easy to avoid. In some cases you could even get infinite money and never die by just going to the left and right of the screen, keeping the x key depressed, and get money from all the side-enemies of the boss coming from the top of the screen.
It would have been cool if there were multiple endings.
So hehe, my text about the bad parts was longer than the text about the good parts, but my 5 star score should show how awesome I find the game! :)