In terms of design, it's pretty much linear with a few enemies as obstacles. The enemy placement isn't awfully bad, but the way the level has been designed didn't bring much fun, and it ended up being pretty boring. The hack is also very small, it could be done in a matter of minutes. Yet, this could be a nice hack for the unexperienced players.
Aesthetic-wise, the original vanilla smw has been used. The only different element I spotted is the Switch Palace's BG, which I believe it uses a vanilla tile combined in a certain way to obtain the BG used there. Besides this, not much can be said about it.
As only misc issue, I'd point out that the castle level suffers from sprite tile limits issues.