The smallest metroid you will ever play. Made this using unity in about a day. This is a webGl version you can play on itch(https://nitinkumar25195.itch.io/thesmallestmetroidever) and newgrounds(newgrounds.com/portal/view/709662)
It's really broad to just say level design, but you mentioned that it is prototype so that may be the case.
UI is cool. Controls felt good and responsive.
I am not a good critic so do take this one lightly. The physics felt jittery at times. Could be many reasons for that.
I think it is a good prototype to build upon.