For anyone on the fence about MM9 right now, do yourself a favor and watch this in-depth piece from ScrewAttack. 

It includes a great rundown of the powerups, achievements, etc., and you see a lot of the levels themselves, but the real treat is Stuttering Craig's impassioned commentary.  He is a great advocate for the power, grace, fun, and challenge of OG 8-bit inspired games in a next-gen world. Get religion now!

Best quote:  “I gotta say, Capcom really knows how to listen to their fans, and listen to the input from them!”  MM9 action starts around 8 minutes in.