Miyamoto has said Galaxy 2 will have less story and has also said he didn't want so much story within the first Galaxy (the team at EAD Tokyo fought for it).
I really didn't see the story and cut scenes as that much of a problem. Maybe this is because I played Super Paper Mario, so I know what true cut scene pain consists of.
8 million is certainly not failure status, but I would use the following reasons for why it didn't break 10m:
1. It's 3d. Not only that, but it's wonky, upside-down, nausea-inducing 3d.
2. It wasn't a launch title, was never bundled, and hasn't really been the main reason to buy a Wii (at least for non-gamers, Wii Sports and Wii Fit are definitely the major games).
3. Too cute and kiddy, at least with marketing. Mario Kart Wii was brilliant because it was in a plain white box with the only colors being Mario and Luigi on the cover. It was able to appeal to adult gamers as well as children. Mario Galaxy had a cute yellow luma on the box with lots of sparkles and colors.
4. Despite it appealing to kids, it wasn't a kid-friendly game. The gameplay and controls are too complex. At least for the kids that I tried showing this game to, they just couldn't get the 3d, planet-spinning gameplay.







