I read an interview where a dev said that he hopes "people who love games" will play it for 10 hours. Which suggests there's 10 hours worth of stuff, but some people will be tempted to skip over some of it.
They also say the game is just under 40MB, but that might change. I'm also expecting some kind of new storage option to be made available around WiiWare's launch. Especially since Nintendo announced their upcoming pricing model for DLC and pay-to-play. They're either going to increase SD card functionality or they're going to add some kind of USB drive support.
"The worst part about these reviews is they are [subjective]--and their scores often depend on how drunk you got the media at a Street Fighter event." — Mona Hamilton, Capcom Senior VP of Marketing
*Image indefinitely borrowed from BrainBoxLtd without his consent.
