I've had the game since 7pm last night. It's weird that the Club Nintendo PIN is printed on the back of the cover insert. This is the first game I've purchased with that. The last 3DS game I bought was A Link Between Worlds which had a separate insert for the PIN. Not a big deal, just something I noticed. Some thoughts and impressions:
I changed the controls immediately. Y - Special, B - Attack, L - Shield, R - Grab, and tap up to jump turned off. I found myself accidentally pressing the default controls from the demo a few times, but I adjusted pretty quickly. Tilts are a bit difficult to pull off with the Circle Pad. The game is not really conducive for competitive play. I don't even mean tournaments. There were times I had to stop myself and hold back because I thought I was being too rough with the Circle Pad. The game works better in a casual oh-look-Smash-Bros-on-a-handheld way.
While I haven't tried every character, I haven't come across one I dislike, including veterans. Bowser, particularly, was not completely awful like he was before since he's at least somewhat mobile now. My friend hated King Dedede, but I haven't tried him yet. Of the newcomers, Little Mac is probably the worst I've tried (I've unlocked half of the remaining characters, most have been clones). To clarify, I don't dislike him, but he's going to require a lot of practice due to how terrible his air game is which, amazingly, is worse than I expected even with Sakurai openly admitting that Little Mac is truly awful in the air. I'm not even going to bother on 3DS due to the controls. Understanding the intracasies of spacing and dodging with Little Mac is going to require more precision than the Circle Pad allows. Oh well.
The best newcomer so far is Wii Fit Trainer though I kind of want to say Zero Suit Samus who has been changed so dramatically that she's practically a new character. And thank Jebus that Pit finally has some finishing moves now. I don't want to dwell on specifics about characters just yet (another time).
I only played one on one multiplayer. It worked really well the vast majority of the time. It only lagged once briefly and we played for about two and a half hours. That's a good sign. This friend is the only person I see regularly who will even have the game so I don't foresee myself playing three or four player matches too often. I only tried Smash Run once to complete the box on the challenge board. It's okay, nothing to write home about. Smash Run is handicapped by the lack of customizable options and the fact that you don't run into other players. For a series known for options and chaotic fun, it's strange that Smash Run is so limiting.
The other modes are standard Super Smash Bros. fair. Trophy Rush was odd. I tried it to complete a challenge, but I didn't really know what I was doing. In any case, the 3DS version has far less total content than Brawl but much more of the content I actually want: characters, and stages that don't suck. Still, as far as stages go, Mushoomy Kingdom is probably the worse so far because it was also terrible in Brawl. I didn't get far enough in it, but I heard they at least removed Level 1-2 so it just cycles Level 1-1. It would have been nice if they made it look like 8-bit Super Mario Bros. so it'd at least be fun to look at. I digress. The best new stage is difficult to pick because so many of them are f-ing awesome. Without spending too much time thinking about it, Magicant (even with the stage hazard-esque characters you can punch in the face to help fight with you), Mute City, and Dream Land immediately come to mind.
Ultimately, it's already better than Brawl, far, far, far better than Brawl. I already knew this from the demo. Still, the 3DS version feels like a demo of the Wii U version. I'm probably more forgiving of this since I'm paying less than $8 for it.