The game is a nice metroidvania, although I feel like some of the powerups felt obsolete (mainly because you can push any block with big mode and destroy all the brown ones).
I could not finish the game without the bigmode infinite jumping, because even in small mode I could not reach the platform that leads you to rocket mode (I also couldn't figure out a different way of getting up there or through the spike pit). Also very often when I was trying to crush enemies with big mode I would get hurt pretty often, which made me want to avoid enemies all together with small mode. I like that each powerup has an immediate use for them when you obtain them. As others pointed out, the lack of music and soundeffects does take a bit away from the experience. I think all together you made a good game and I think with a bit more development time you would make it a great one!