Can't think of any 8-bit FPS games (and I'll admit I'm in the camp that thinks this Megaman thing looks kind of bad, but I'm not hating the OP for it

), but if anyone wants a little anti-brown and gray, there's a good Team Fortress 2 mod out there.
http://wiki.teamfortress.com/wiki/Parkour_Fortress
Parkour Fortress is an attempt to recreate Mirrors Edge in TF2. It has some rooftops levels, some references to Mirrors Edge maps, and a few of those pretty abstract block things from the Mirrors Edge DLC. The physics take a few runs to get used to, but they're pretty functional, and you play as the Scout so you can double jump! It's a really addictive mod and definitely my favorite user-made TF2 thing. Try it if you AREN'T AFRAID OF FIRST PERSON PLATFORM JUMPING!
EDIT: Forgot to mention that link has a direct link to the servers that run this mod. I only know of two of them, but they typically have anywhere from 10-20 players at a time.