The first thing I noticed about this game is how incredibly bad the frame rate is. Everything moves at a snail's pace and moving your player feels like you are walking through a pool. The music in this game is downright annoying on many levels, the notes are all over the place and it feels like the songs were just slapped together out of random notes (not to mention, the music does not loop properly). The sound effects are as basic as you can get for games trying to be "retro", it's monotonous but the sounds themselves aren't particularly bad in their own right. The graphics are also very basic as Mario clones go, but my biggest complaint is that there isn't enough detail in the backgrounds. These graphics feel more like Super Nintendo than NES which is fine, but if you want to go in that direction you really need to put at least a few extra details. Like for the overworld stages why not add a few mountains or a waterfall? Something to give the game more "depth" instead of a blue sky with nothing but emptyness for miles and miles.
I'm not saying this game is downright terrible, I'm saying that it needs quite a lot more work done on it for it to be considered a decent Mario-clone platformer.