Looks like the natural evolution of Super Mario 3D Land, one of the best games for 3DS... in short, I'm pretty stoked.
A couple of points worth noting in that trailer:
* Anyone spot the Green Stars towards the end? I'm one of the few people who enjoyed getting all of them in Super Mario Galaxy 2, so I'm interested to see how they are incorporated.
* Hey, look, an actual substantial boss battle! That was one of the few obvious bones to pick with 3D Land, with the very basic, repetitive Boom-Boom and Bowser fights. Good that 3D World is taking a cue from Galaxy in that respect.