Just played through Trip World (gameboy) on my 3DS, I'm sure it's been brought up here before because it has some of the best pixelart from before the gameboy colour and also some of the best gameboy music.
Here's a video, the video doesn't correctly show some of the tricks like flickering sprites/etc but it's still a pretty good video. Best $5 I've spent in a while, it's not the longest game but it has some decent challenge, a lot of charm, and curiously most of the other critters in the game don't try to hurt you, though some do if you attack them first.
I never heard of this game before so I thought I might as well mention it here, it could make for a good PA analysis thread or something someday.