Tanooki suit, weird blocks, and Roy Koopa. Word.
http://www.nintendoworldreport.com/impressions/26608
Super Mario 3D was playable immediately following Nintendo's press conference. On display were four levels, three regular levels and one airship level. Additionally, the Tanooki and Fire Flower were available in the demo, with a large focus on the Tanooki suit.
However, the suit was limited, with only a Yoshi-esque hover and a tail whip. Basically, it's the Yoshi suit. Luckily, the power-ups aren't timed, and the Fire Flower is rather nice and reminiscent of its use in Super Mario Bros. 3 and other 2D games.
Don't be confused, though. This is a 3D Mario adventure, seemingly more similar to Super Mario 64. The first level, labeled 1-1, was a little claustrophobic, as your movement felt limited and the gameplay was slow. The camera seems almost too close, though the level does show off some nice 3D effects. These seemingly optional segments appear to be quests for Comet Medals, which unlocked additional stars in Super Mario Galaxy 2. One of them in the first level reminded me of the Pogo Cat 3DS demo from E3 2010. Basically, the blocks were a indecipherable blob in 2D, but were crystal clear in 3D, showing you a path to the top.
The second level, labeled 1-2, was underground, and featured the Fire Flower heavily. There were a few cool uses of 3D in the level as well. The coins in the level popped out, and were also activated by a familiar P Switch Block.
The third level, a later level (3-3), had a unique mechanic where you stepped on switches and timed platforms folded out of it, opening up new paths and puzzles. This level was a lot more freeing than the first level, which was nice. It also used teleportation blocks that moved you around to different rooms and areas, kind of like the stars that shot you off to different planets in Super Mario Galaxy.
The final level was an excellent airship level. It automatically scrolls, and is primarily side-scrolling as well. It's like those airship levels you loved from earlier Mario games, complete with wrench-throwing baddies, Bullet Bills, and fire. The boss, apparently Roy Koopa, was simplistic, but fun. It's the first time the Koopa Kids are in a 3D Mario game, so that's awesome. I love me some Koopa Kids.
I liked the feel of the game, though it feels very different from Galaxy 2. It's truly reminiscent of Mario 64, for better or worse. I'm very excited to see more of this game, and what I saw, I really liked.