Yeah, we saw that level select screen too.
During the Nintendo Direct Pre-E3 showing, behind the new, exciting console news, some brief shots of what looks like a more complete version of New Super Mario Bros. Mii were shown. We don't know whether they'll keep the name of last year's tech demo, but the game is certainly the Wii U iteration of New Super Mario Bros.
Now, assuming these screens were from the real game, we have been given a lot more information than initially apparent. There was one quick showing of in-game footage, which looks like a more detailed version of what we've seen already, but as some of you have noticed, a world map for the game was also shown.
From the footage of the actual game being played, we have a few things revealed, confirmed, and reconfirmed. Star coins are obviously making a return, and after Mario loses a life, Bowser's face appears, suggesting—as is the case with almost every other Mario game—the Koopa king is bound to return. Also, we see a castle in the background, likely Peach's, suggesting we are in the first world, as well as some slanted pipes reminiscent of Super Mario World. There's also a looming, slanted mountain structure present during the stage, which also shows up on the map screen.
Now, onto the fun stuff. In the level select screen (which bears some resemblance to that of Super Mario World) we see the standard New Super Mario Bros. fare: Toad Houses, 1-Up Houses, stage spots, and what have you. The interesting part comes in the statements made by Miis on the level select screen. A male Mii named Thomas says, "OK, being a flying squirrel is WAY more fun than it should be!"
At first glance, this sounds like confirmation of the Tanooki suit, though the use of the word squirrel may suggest a new power up with wings like that of a flying squirrel, especially when you consider the likelihood of Nintendo having a Mii on promotional material getting the suit mistaken with something else.
The next interesting thing happens with a Mii named Michael. He says, "A baby Yoshi that balloons up to carry you? Too cute!"
Again, this person uses proper capitalization and is on promotional material, which makes two things clear. The first is that Yoshi's are likely returning to the new game; the second is that there are new types of Yoshis, including baby ones that can balloon up (perhaps like in Super Mario Galaxy 2) and likely carry the player to new locations (maybe over large gaps).
There is one more Mii statement, and although doesn't look like anything special, it may have confirmed a suspicion about the system many of us have long had. This Mii, named Catherine, says "Nice! I finally did it, and I did it under 100 seconds! I RULE!", but above that, it says in a gold box, "Cleared in under 100 seconds!"
This could hint toward the existence of an achievement system of some kind. And if you notice, this isn't a regular level either. Under the text, you'll see the bottom of what is clearly a castle of some kind, likely housing a mid-boss.
Lastly, in between levels at the top, we can see pipes with flowers on the top. Could these represent special underground levels? Could they be connected in the same fashion as Super Mario Bros. 3? At the very least, we may have to wait until Nintendo's E3 press conference to find out.