Love it! got to level 4 and I'm like "uhh am I missing something?" to come back here and find there's just the 3 at the moment.
I think to build on the concept you have for more levels, after the basics, make them require a bit more timing (you actually do this with the star in the middle but building on it). Maybe jumps or falls blocked by an enemy going back and forth that you need to time?
I think once you add sound and SFX it will help make it POP! Look forward to seeing what you cook up!