Demakes are just plain fun. I'm sorry, but reimagining a game for the past can be some of the most clever stuff you'll ever see. For example, take junkboy's work over at Pixelation. He shares an impressive amount of demakes he's done over the years for a Swedish gaming mag, and plenty of them are simply genius.
Turning Killzone into Contra is one of the best, though there are plenty of other great standouts. I love Dead Space as a Game Boy game and would gladly procure a portable, side-scrolling, 3D Dead Space game if one happened to land on the 3DS. I also love the idea of Bayonetta as a shmup and BioShock as a Castlevania clone. Then there's Brutal Legend as an adventure game!
You know what? I love them all. Hear that, game developers? Demake all these games right now.
Demake dump [Pixelation]