On paper, this all sounds really good, but in practise, I spent a good chunk of my time in Super Mario 3D World accidentally falling in chasms or landing right next to enemies I was targeting. And if I trust the dedicated NeoGAF thread, I was very far from being the only one.
Super Mario 3D Land is called Super Mario
3D Land because it has stereoscopic 3D, so its more or less isometric design didn't cause any trouble in depth perception, and I never, ever landed Mario or Luigi anywhere I didn't expect them to. In 3D World, on the other hand, the forced "isometric" viewpoint without stereoscopic 3D caused tons of depth perception problems or optical illusions resulting in many "what?" deaths.
Add to that the weird handling sticking characters to 8 direction movement and the weird way running speed is handled (walking speed, then press the run button, then first running speed reached, then run for a bit, then second running speed reached), and you have an unintuitive mess that results in tons of errors.
Don't get me wrong, I had a lot of fun with Super Mario 3D World, and after I started obsessively looking at my character's shadow, I could avoid a lot of deaths. But ironically, to me it was the exact opposite as you say here:
Far less about exploration and far more about a series of platforming challenges.
I actually had fun in Super Mario 3D World as long as I looked for all three green stars and each stamp in each level. The moment I completed that task and ran to the end just to beat levels or improve my best time, my enjoyment took a nose dive, because after you take the surprise factor and exploration out of the game, it's rather dull and not very fun. Whereas I completed Super Mario Galaxy and Super Mario 3D Land twice in a row (Mario then Luigi) without such issue.
The fact the main costume of the game allows you to
climb on walls should tell you platforming isn't as much a main factor as you think it is in Super Mario 3D World.
Also, I loathed the 8 direction movement and the speed threshold thing. Caused tons of deaths and made the characters just unpleasant to control. There is also no sense of universe in this game, sure, it's imaginative, but it all feels like the result of desperate brainstorming sessions glued together without any sense of cohesive whole - a bit like Super Mario Galaxy 2, actually. Everything feels arbitrary, whereas Super Mario 64, Super Mario Sunshine, Super Mario Galaxy of course and even Super Mario 3D Land, despite their weirdness, all felt like they belonged to one consistent vision. Hey, even Captain Toad actually makes a much better job at it too despite its wild creativity, you get attached to its world and characters whereas Super Mario 3D World feels like Mario Party.
Also, the end boss sucks. It's just a cinematic set piece.
Finally, two observations:
1) Super Mario Galaxy also managed to adapt 2D gameplay to 3D, its gravity gimmick being just an elegant way to control the camera and always orient it in a way where you see where you're landing, and this while having a very rich world with some freedom and a real artistic vision. And Super Mario 3D Land is IMO a much better "get to the end through platforming" game than Super Mario 3D World.
2) A lot of things I dislike in Super Mario 3D World are caused by the multiplayer. Multiplayer implies the forced perspective, the 8 direction movement, and probably the speed thresholds to accommodate to beginners. With this, Nintendo hurt the game for probably a VERY small audience, the percentage of people really playing this game in multiplayer being surely a very tiny minority. Make a multiplayer mode or something, but stop hurting the single player because of a marginally used multiplayer mode.
Really hope that Nintendo will make a 2D Mario with the level of fun, creativity and level design as 3D World.
It's called New Super Luigi U, IMO a MUCH better game than Super Mario 3D World.
In a nutshell.