Nah, I don't think it'll be hard for them to top. They just need to keep doing more of what they were doing... and I don't mean the whole flying around in space thing, I mean sticking primarily to obstacle courses from point A to point B with some variety of oddity stages spaced between them. Add in some extra power for better visuals and more elaborate physical objects/toys and it should be pretty trivial for Nintendo to outclass Galaxy. Case in point: They already basically matched it with SMG2.
I feel it can be done, it won't be easy though, because Galaxy and Galaxy 2 are both masterful games. --- Want to help bring Fatal Frame Deep Crimson Butterfly to NA?Join Operation Zero https://www.facebook.com/pages/Operation-Zero/131582506953973
They can do it Super Mario Galaxy 2 was damn good but not perfect the better question is will people accept it as being better than the Galaxy games? --- THE EARTH WAS STOLEN!. 3DS: 1418-6790-0913 (Reg)
The Galaxies are severely downgraded from Super Mario 64, so it will be super easy to surpass Galaxy. Unless, of course it turns out to be SMG3 :'(
Well at the very least, thank freaking goodness for the tablet controller and no gimmick motion wiimote for single player! --- You might want to get thicker skin if you are unable to handle the opinions of others.