Visuals
1 ... GUI works very good with mouse interactions
2 ... for my taste BG is too static
3 ... coin animation good animation -> gives some feeling/movement to the game
4 ... those "star" spikes looks like BG
5 ... BG does not fit best with FG art
Design
1 ... Is "main menu" your title? (wait its not)
1.1 . Change "main menu" to the title of your game
2 ... (check Controls 2.): Problem is if player does not read tutorial (good chances) that they gave up before coming to good part.
3 ... rng coin spawn very good
4 ... maybe create level which is tutorial:
4.1 . level is gifted as player points (cant die, easy, only gain, contain core mechs. required in next levels)
Controls
1 ... character movement very responsive + sound effect very good
2 ... interesting mech: after you realize you can fly game becomes enjoyable
Sound
1 ... click fast menu -> settings: you sounds OST/BG sound gets restarted all the time
2 ... BG sound becomes repetitive after some time of listening (1min)
Bugs
1 ... coins spawns inside walls