The first point is something I've been thinking about for a while now. All of Galaxies levels felt like far out extreme planets and worlds in Mario's universe, the over-arching theme of space brought it all together and the game felt like a giant adventure. Ironically 3D World does have a few levels that feel like they're part of the actual world, case in point the very first one, but then it just drops everything and the game just starts throwing random level designs at you. Which is weird since so few Mario games are themed like this, even SMW bases it's levels partly off of certain aspects of the overworld,
I just don't understand why they are theming and designing the levels like that, it really destroys immersion and makes the game feel like just a collection of levels. But I guess that's just another thing about 3D World that bugs me, I mean imagine how cool it'd be to see different locales of certain levels on the world map in the background of the train levels.
Ultimately, what people fail to realize is that a game is more than just game-play or resolution or controls, it's an experience where every little thing counts.