MM8 - Make it not suck.
Not to sound offensive, but I guess you may need to first list things before saying that.
Here are my thoughs:
MM8:
Tengu Man: Don't liked rush jet area too much. I would stick with the typical Rush Jet item. The wind was a great effect, though.
Grenade Man: Don't liked the hammers. I guess that's the only thing to mention here.
Clown Man: It's level design was great, though overall it doesn't look to megaman-esque. I would change a few, but not all textures.
Frost Man: Keep it. Snowboarding could be better without slopes, though. I hated slopes since the start of megaman.
Sword Man: His level is way too gimicky.
Search Man: Great level. It's the only one that I really like.
Astro Man: way too much enemies and dissappearing platforms in the outside. I would keep some section for more megaman-esque gameplay. Don't liked the tower gimmick either.
Aqua Man: The midboss was annoying. Anything else is fine, except for the robot master itself, which has an annoying voice.
Dr wily: Delete rush jet and snowboard gimmicks here. More megaman-esque gameplay here, with the typical wily underwater section and a different gimmick.