Simple yet effective.
Collecting crystals is very satisfying, the shield powerup is surprisingly fun to use, the hearts falling down give a much needed incentive for quick and less thought out gameplay, the fact that you can pause your movement but then commit to shooting across the screen consistently creates interesting choices, the powerups are well thought out and have great synergies, you somehow made it very apparent when you lose a life in all the chaos and lastly the way the shooty shooty things increase in quatity each time you cross the screen is very clever.
I didn't realise until I beat it that the "jumps" in the left bottom corner was the end goal, making me struggle to realise the importance of health and shields for much of my first playthrough. Secondly I didn't realise until I got the hold space to slow time upgrade that you can hold space to aim better.
LASER SIGHT I thought would've been more useful than it was. I thought it would show a red line where the triangles were gonna shoot, and then the line gets thicker the closer they are to shooting. I think that would've been very useful, cuz currently there's so much vital information spread in all corners of the screen. While this may be by design, the rest of the game design doesn't strike "I want to induce as much stress to the player as possible" as much as this does.
Other commenters have suggested an attempt meter, which I don't think is necessary as it promotes overly careful gameplay. Though something to tell runs apart would be nice.