Now that was a really good and fun game!
I love just how complete and polished it is, it's got everything! Multiple stages, each ending with a fairly well-designed boss-fight, it's got an intro and ending cutscenes, passwords, really good, well-drawn and well-animated graphics, really good music and sound effects, and I especially love how you not only stuck to only one BG layer, but you also kept your palette consistent, even when fading the screen in and out, just like a real Game Boy!
The only meaningful complaint I have is the fact that holding the Jump button makes the character jump constantly, like when you land, if the jump button is still held, the character will jump again immediately as soon as he touches the ground, that's rather annoying, but it's fairly minor all things considered...