Oh wow, this is awesome feedback, thanks! I like that you already managed to get to the end (aside: I am very bad at my own game). The levels not feeling "special" actually came up with someone else and it's something I never thought about. The other tester mentioned that it didn't seem like there was much different between levels besides the colors/etc and that's (mostly) true. I think it was just me making a video game (ice level! water level!) without really thinking about it. There's not really supposed to be a ton of variation between levels but I might try and do something a little more involved. There are small limits on enemy spawning (no exploding enemies in the first two or three levels) but I might go further thanks to these suggestions.
I will have to see if I can figure out what caused that freeze. Not good :(
The biggest takeaway I've gotten is I need to provide more feedback to the player as to what is actually going on in the game. It's super hard for me to evaluate the game in that way, which is why getting fresh eyes on it is amazing. I've already got some ideas and I'll need to make a bunch of (hopefully not huge) changes that will hopefully make it feel better. Thanks a ton for taking the time and playing and writing all this down. I super appreciate it! I'm excited to put some more work into this thing.