I'm hoping that Mario128 is just a couple hundred levels like the Special ones were in SMS. No backpack. Just me, Mario, and an infinite drop underneith, with a bunch of remixed old-school mario music going on underneith. Get from one side of the level to another without dieing. 10 or 15 of those and then some sort of boss level. Sorta like a SuperMonkey Ball, except relying on platformer skillz more than on puzzle solving. That and I hope they bring back some of the old powers. Fire Flowers raccoon suits and whatnot. I don't think those have been done well in any platformer I've played yet. They always seem like additions to the main gameplay instead of being part of it.
I loved Mario64 a lot, and I played the hell outta SMS when it came out, but it just seems like we ain't really seen a 3D Super Mario Bros. game. Instead they invented this new genre, which is hella fun, but it's a lot different than the old goal of get to the end of the level without getting hit or falling.