Very good game, Here's my review
GRAPHICS: graphics are limited, yet nice and retro. not much else to say.
PHYSICS: when you hit a block it feels just like a regular Mario game. but when jumping normally, you fall, and like a brick. (also the jump is too short)
GAMEPLAY: level design is great. simple, yet not too simple. Koopa shell is VERY clunky.
SUGGESTIONS: Add music, and more level themes like ice, forest, sky, and also add lava to the castle levels. add some of those toad minigames from Super Mario Bros. 3, and that's about all i can think of currently.