I think the star missions, or "levels," should be linear like Galaxy, as I agree the tightly focused platforming serves the gameplay best... But I think the overworld should be as huge as Sunshine's Delfino Plaza, with ONE major difference: at any time you can instantly access a Level Select screen.
See, Starship Mario was great in how it allowed you to quickly access levels, but it was a lifeless overworld in and of itself. I don't want want to give up the Level Select, but why does it and a robust overworld have to be mutually exclusive? Hint -- they don't.
Having a Delfino-grade overworld would allow players to have fun simply running, jumping and wall-jumping around. At any time you could hit Start, or head over to one of the copious Warp Pads littered around the overworld, and access the Level Select, just like Starship Mario. But unlike Starship Mario, if you wanted to explore,
there'd be something to explore. All the convenience of Starship Mario; all the depth of Delfino and Peach's Castle. It would preserve the sense of exploration, of adventure. And it would anchor the game in a sense of
place that was sorely lacking from SMG2.
Frankly, I've already forgotten most of SMG2. It's fun when you play it, but when I look back on it, I can't tell you the name of a single level, or what levels were clustered in which worlds. They're just a bunch of disassociated realms, each one over before you know it. It makes the game as a whole feel fragmented, unfocused, and less fulfilling. Though I think SMG2 had better levels, I think SMG1 still feels more EPIC because as unfunctional as SMG1's overworld was, at least it had a sense of place that created a warm, central core to the whole experience. A place with magic.
I also think that, in addition to having a huge overworld (one that again, has Level Select available anywhere at anytime), there should be some cohesion to the "worlds" in which the "levels" are clustered. For instance, the last world could be a "dark" world in which each of the seven Koopalings -- and Bowser -- have their own level. Each level would be a riff on the castle/haunted theme. Perhaps each Koopaling has one key to the Bowser galaxy at the center. Defeating them all opens the way to the final boss, creating a sense of progression and -- wait for it -- adventure. Like you're actually going someplace.
I think this is a good compromise between the two styles.
