What I liked:
-The minimalist art is simple but amazing
-The music fits nicely
-The metroidvania is really well applied, kept me going for a while (didn't finished, explained later)
-The map is a HUGE help
-The powerups are simple, but cool, the "swaping" overall was interesting with clever puzzles
-Everything is introduced progressively, made it easy to undertand
What I didn't like:
-After the first time I died, all of the sound just stopped (reloading the page fixed it, but lost the progress)
-After some time (after the circle boss) everything became REALLY laggy, to the point the powerups worked half of the time, and made it impossible for me to finish it, and when I reloaded I lost all progress
-> Saving didn't work, but I was on web so probably that's why
-The rolling spikes bugged sometimes and just went rolling wherever they wanted, it was actually pretty funny but I wanted you to know