It's a fun game, and it definitely does look and sound amazing, so congrats on that. The custom overworld looks nice too.
That said, I have a few issues with it:
1. The levels are just too damn long. Sometimes this works, but often it feels like levels just drag on and on with little variation and it gets boring. This is especially bad in autoscroll levels or that one underground one.
2. The custom sprite choices are kind of boring. You've got the odd enemy from the original sprite tool, and a bunch of the more basic default enemies from Mario World, but you need more variety. Maybe try some more interesting default sprites and combinations, or use some more recent custom sprites from SMW Central. The current enemy choices don't really suit the levels.
But it's a pretty good game. Just one that could be made so much better still with some simple changes.