I like how in the end, when the UFO boss arrives, the player faces a dilemma that previous enemies were all killing them on touch, so what does he do with the boss? Typical way of doing it would be a tutorial UI: freeze frame, draw arrows and red circles, display "jump on top of the UFO" message and do other annoying stuff developers these days do to command their user as if they had intelligence of a toddler.
But Ismael found different way of doing this. Simply don't spawn any new objects so that the only thing that's left to do is to jump on top of the enemy like in "Mario" and hope for the best. And it's so much more fun and rewarding, especially considering there's a satisfying animation and a high jump that follow. Design decisions like this is what makes games fun.
The only thing that this game needs is some lush/animated backgrounds instead of blackness, mainly because 90% black space preview looks a bit dull and I honestly clicked only because it was an Ismael's game. And it was very pleasant experience! Which I could have missed. So if there every a full version maybe this can be considered.
Anyway I'd rate the game but don't see the corresponding button anywhere.