The following is something that I posted on another forum about my thoughts on the game.
Oh my lord at Super Mario 3D World, I am so fucking excited for that! Super Mario 3D Land was a damn good game with an amazing concept for 3D Mario (linear 3D Mario that has 2D Mario mechanics), but it felt a bit undercooked mechanically and level design wise, especially with all those repeating levels. This is because SM3DL had a rather rushed dev cycle.
From what I saw of that trailer, this game already looks quite improved. I see a lot more variety in level design, mutliplayer looks fun, Cat Mario looks like a great and unique sort of replacement for "flying" that fits 3D Mario, and Mario, Luigi, Peach, and Toad playing differently is something Mario has sorely needed to return for a long time! Finally, level design wise, I noticed that the stages seem to be FAR bigger than SM3DL's, so this game might have a lot more exploration stuff. The smaller levels also seemed to have more interesting concepts than Super Mario 3D Land's sometimes bland level design. In particular, I liked that level with the rising death trap looking creatures, and seeing the Goomba's Ice Skate made me laugh!
Overall, I wouldn't be shocked if this was 3D Mario's New Super Mario Bros Wii: aka, a MUCH improved sequel to the portable original!
Edit: Something I forgot to mention: The great part about Cat Mario is that it fixes a problem linear 3D Mario has had. Flying power ups would be extremely broken in those (though tbh I can see Nintendo making levels designed around it working in 3DW from the levels I saw so far), its the reason Tanooki was nerfed so hard in 3D Land (granted it was still sorta broken there). Cat Mario is perfect, it means that there's a way to sorta "fly" up walls without breaking level design too much! Also, this gives me hope that the game has less of the "boring floating platforms in space" issues that some 3D Land levels have!