Leaving aside the absurdity of a maze in space, this game is amazing. There is a strategic element to the turrets and the enemy wave difficulty ramps up nicely. There is also a good "winging it" element, once you figure out your strategy. As someone who enjoys planning a little bit, but gets burnt out with too much of it, this scheme is perfect for me. The "wave health" bar is a nice, subtle touch (as is hovering over towers to see info on them, instead of having to click.)
I like that the game pauses when you place a tower. This way, you can leave the enemies on "warp speed" when you have just barely not enough defense. Then, place a tower in just the right spot and get rid of the rest of them.
There was a weird problem with lag when I had it set to the highest speed, from wave 40-something. It had nothing to do with my hardware, either, since CPU and GPU utilisation were at 10% and 5%, respectively. Enemies were also showing up where they shouldn't be (on top of towers and outside of the maze.) The game got sort of boring after that, but I played through to wave 75 before deciding to quit.
Still, this makes me want to try making a tower defense game for programming practice, even if it takes me hundreds of hours... Probably won't be anywhere near as good as this game, either, since you seem to have been at it for 3 years.