The hack's levels are largely unimpressive and feel like they've been slapped together with random ideas. The Yoshi's Island 1 replacement starts with a bullshit design element, i.e. jump now or get shot by a Banzai Bill. It's the hardest level in the demo too, which I guess would make sense considering it's the precursor to a bonus level and is not on the "main path to Bowser." The first half of the castle takes place outside and utilizes the same idea as the original's first room, and the inside has a large swimming segment. The only thing I did not like about that was the dead ends underwater being unrewarding, long to get to the end, and high-risk; I found it weird how the Dry Bones would get stuck on one part of the escalators, and the Podoboo placement was still too low.
However, I enjoyed the level before the castle and the Yellow Switch Palace in this hack. The Yoshi's Island 4 level uses the same tileset but throws in Dino enemies; it's kind of rare to see that combination, and it plays alright. The Yellow Switch Palace is a vertical bonus room with some threats in play, but a lot of it involves sliding down hills and catching coins as you fall down long pits.
The hack has a couple of glitches: No event tied to the castle means the exit is not accounted for in SRAM, and the music note block next to the pipe in one level can kill you.
The music is the same as SMW's, sometimes not really fitting the level (the dreamy water music in Yoshi's Island 2) and ExGFX are very sparingly used: you'll see a fresh BG and slopes added to the Switch Palace, SMB2 font, and you'll see SMB3 munchers. It's not completely vanilla, but will please those who like to see Mario games that are strictly Mario.