Great game! I enjoyed it so much! The controls feel great and that's the most important part for these kind of games in my opinion. Just a few things I could see improving:
-Sometimes I completely missed the spikes and just didn't see them and until I stepped on them (regular spikes, not the ones that come out when you touch them). It may be just me, since when I look at them they are pretty visible, they even hace that shining animation...
-I turned off the screenshake because I didn't enjoy it, it made it harder for me to see and play precisely. I'm not a big fan of screenshake and while I found this one particularly annoying, it may be just me hating on screenshake as usual.
-Rocks that allow you to shoot back bullets are a mechanic I don't like: the controls are a little awkward, it didn't feel very intuitive/didn't make a lot of sense thematically (¿after you hit explosive rocks you become glowy and now you can absorb a bullet and shoot it back to turn off laser beams?) and in this demo there's only one use for it (turning laser beams off) which isn't ideal, it's a lot better when you can use a mechanic in multiple distinct ways (I'm guessing this will be the case in the full game, but make sure it feels different).
-And the biggest thing: bigger picture level design was weird. I don't know if bigger picture is what I mean to say: most sections were fun and well designed, but the composition of sections that form a level felt pretty random. For example there were a couple easy sections that don't use the same mechanic (or a new one) after a harder section. Also at times you introduce a new mechanic but then don't use it immediately in the level coming after the introduction, that's unusual. Levels didn't feel like they had an overarching concept, idea or personality.
I'm focusing on the things I think could improve because that's what I find most useful, but I really enjoyed the game a lot and I'm looking forward to playing more of it. Good work, keep it up!