Takes me back.
Let me start by saying, this is a fun game. I'm a bit of a masochist when it comes to gaming, so this was a great experience for me. I didn't make it too far (level 14) so I'll give it another try later. (To be honest, I just couldn't get the hang of picking up those little crystals at first, I felt like they were shooting at me and kept dodging them.)
I can understand why some people are getting frustrated about the game's ever increasing difficulty (minus the little asteroid intermission levels). As long as you can keep from dying, you'll have no problem with each level. Just play it safe =D