What 3D World shares with Mario Land is the wide isometric camera angle (to accommodate multiple players and to make the camera secrets discovery a part of the gameplay). The rest is either new or taking the best from other Mario titles. New moves aside (ability to grab/throw items, mid course boost), playing Toad is a new gameplay mechanic for gamers: he's far more agile than Mario in Galaxy.
It also shares the limited (and inferior) 8-way digital movement and a run button.
It's pretty clear that this game is not what was expected and the arguments in favour of it are reaching at best. (I mean really, "3D Land was 30fps, this is 60fps! It's not the same game!" It reeks of Reggie's "It's not the same content!" line).
When Koizumi & his team made Galaxy, a game that stood up to its peers (on superior hardware) and redefined 3D platforming, with a Gamecube and some duct-tape ;P and the best they could do here is a 3D Land up-port....says it all.
Also having to accommodate 4-players means the levels have to be designed with 4 players, meaning the tight-platforming (that is ironically championed from 3D Land) won't actually be nearly as tight. Or perhaps they did in fact design it with 1 player in mind and added in the extra characters for marketing, in which case they would be undermining themselves. Also the lack of online is hard to understand. Some have said that it's not possible/not same vibe, but anyone that has played either co-op or competitive multiplayer online with friends knows that the "not the same vibe" line is patently false.
It's quite funny that the characters and mechanics for this game, which are being championed as "genuine" Mario experiences, stem from Super Mario Bros 2, which everyone knows isn't actually the real SMB2 game (Lost Levels is), yet are quick to denigrate those that would label 3D World as "not the proper/real 3D Mario game".
Safe and lackluster describe this game best.
A word on the whole themed/worlds level structure topic: one of the best parts of Galaxy 1 & 2 is that they didn't have the traditional 2D setup of a few regular levels >> mini fortress >> ghost houses/regular levels >> main fortress (rinse and repeat for 7/8 worlds). However, 3D Land did, so it would be disappointing if 3D World incorporates this structure. (Galaxy was great in that it created a desire to see what the next level would be, but whilst still including the ghost houses and (mini) fortresses).