Hooray, gamepad controls! :)
I managed to get all the way through the game. I think I agree with most of the comments below on the enemy speed, etc.. really, I think balance is the main thing the game needs a bit more of.
In particular, the game felt a bit tedious, which I think is due to the 10 separate hives combined with a total lack of progression in terms of upgrades or enemy types past the point where you get all three upgrades. I ended up actually defeating the hives early on in the game last, as I went back to try to destroy the wall next to the UFO, and then exploring that whole section took a long time, and then I still had to backtrack to the hives that I had seen before obtaining the gun.
I think, however, the main problem here is actually permadeath. I don't think the game ended up actually being that long, but I was certainly stressed out over dying and losing all my progress. I think the game felt a lot more tedious because I was internally like, well, if I die, I have to do this all over again...
That said, permadeath did make the game feel more tense. But I personally do not prefer it.
An interesting phenomenon is my perception of the enemy health. I read in some of your other comments that they only took 4 hits to kill, and I thought that must be way off as it felt like they usually took like 20 bullets or more... when I went back and counted the enemy did only take 4 hits, but it definitely did not feel that way when playing the game. Perhaps I simply missed a lot of shots because the enemies are moving so fast..? Or perhaps there are usually a couple enemies on a floor, and so the shots are absorbed into several instead of focused on a single enemy, making them all take a seemingly long time to kill..? I'm not sure. Either way, I think making enemies *feel* like they only take 4 hits would be an improvement. My guess is the best way to do this would be to make them move slower.
That said, the core gameplay is pretty solid and fun. I think my perception is filtered a bit by the permadeath as mentioned--it just obscures the fun of the game by making me stress out. I'm also not a big metroidvania player, but the metroidvania formula worked well as far as I could tell in this game. Getting the boots was a nice upgrade, and when I decided to go back to the UFO because I knew there were some high platforms above it, and got rewarded with the shield, that was pretty nice.