Well that was certainly an experience.
The last few levels were really exhausting, but I pulled through. I'm really not much of an action gamer, so for making it through every level, I'm feeling quite proud of myself right now. Enjoyable, great music, and all-around solid game.
Now then, on to complaints, because no game is immune to my pessimism:
* Gate-switching could get really confusing at times. If it were at all possible, I would appreciate having an option to rotate the field 90 degrees counterclockwise, so that the number keys match up with the gates, left to right.
* Freezing power-downs are more of a nuisance than they're meant to be in the last few levels, because more than likely, before the gate thaws, another will fall on you and reset the duration, with no way to stop it from happening. Lucky for me that I had a ton of lives and a devastating laser, or things would have gone south quickly. Also, I fear that it's entirely possible to be caught in an indefinitely long freezing barrage, with no hope to escape. Unless there was a hidden variable protecting me, I would implement a fail-safe to prevent that sort of thing.
* I was let down by the fact that my only reward for beating Level 12 was a loopback. I would have preferred a celebratory victory screen followed by a return to the main menu, to let my accomplishment sink in. Or at least, separate the game into a 12-level mode and an Endless mode.
Anyway, I think you've gotten enough criticism. Again, really, really great game. Tons of fun. Can't wait to see what you come up with next.