GoNintendo has posted some YouTube videos that show off test versions off two canceled titles: Resident Evil for the Game Boy Color, and Resident Evil 2 for the Game Boy Advance. For a little comparison shopping, here's the full intro to the Nintendo DS version.
While the GBC version is pretty much what you'd expect, the GBA version looks pretty darn good. Sadly, development was later canceled on both of these. It makes you wonder what else is out there that almost made it. We're usually only able to see the final versions of games, and some of them shouldn't have made it that far.