I ran into one of these when I visited Irvine and I got to play a bit of Smash Bros. 3DS. It was a lot of fun, even if it was just 2 1/2 minutes of playing.
Since I posted in the middle of a discussion and experienced pageloss, I'm gonna just quote this again, and also my initial impressions of the game:
1. The menus, even if being worked on, are rather nice and it feels like I'm playing Melee.
2. Megaman's moveset is unlike any other character I've played so far, and I horribly lost to a lvl. 6 Marth due to me having issues reaching the smash ball.
3. The gameplay is really smooth, even in 3D, which surprised me a little.
4. Just like the character/stage select, the gameplay itself felt like Melee with very fast and fluent movement, unlike Brawl which had floaty characters and tripping to "balance" some of them.
5. The victory screen looks a lot like Brawl, but appears to only show the victor up-close.