Wow, great little game!
Not much to say about it, it's just some good ol' classic Gappy fun but in a GameBoy flavor and I had a good time playing it without any major complaints. Presentation was charming, music was cool, levels were fun and challenging, love the way the mechanics were varied in each world, jumping felt good and I didn't have any botched jumps due to bad inputs or anything like that, and so on: it's all that and a bag of chips!
If I had to search myself for some sort of complaint, it'd probably just be that the difficulty curve can be a little awkward: I definitely felt like the space gravity world should be switched with the circus world in terms of order, and some levels here-and-there were serious spikes in challenge. I also wish there was a save/load: I know it can be a short game technically but still, a continue is always a nice thing to have. Oh, I also felt like the special effects were lacking in some departments: for example I was surprised there was no water splash when you fell into water. Also thought it was kinda weird that you don't jump with space considering the game gives such credence to it, but eh, it was easy to figure out.
Anyway, overall well done!