I played the demo for about an hour or two. Now I understand that the 3DS controls will inevitably suck, but what can you do? I never noticed any FPS drops. Online videos and twitch streams don't do the game justice in that respect. Overall, it's a fun portable game.
Is it a fun competitive game? No, not really. What's the best way I can put it? It feels...incredibly unsatisfying to kill anyone in this game. People die at really high percents, blast zones, etc. I think we've all been over this. Now, I understand that this game has an increased off stage component. You have to go and "earn" your kills by jumping off the ledge, spiking, etc. But not all characters are well equipped for this style. Link, to my knowledge, lacks any spikes. His recovery, though not terrible, won't save him when he really has to go off ledge to kill someone. So with Link, you're stuck on the stage...in a game that now requires you to go off stage. Characters who don't have spikes or good recovery options will probably have a hard time in this game.
People seem to rave about the off stage mechanic, but when they start hosting tournaments for this game, I wonder how many top level tournament players will go off stage to secure that kill? If you had $1000 on the line, would you take that risk? It's a difficult question to answer. But my guess is that even though this game is designed for off stage play, tournament players will not be taking those risky maneuvers. Long story short, killing someone requires a lot of effort, and does not feel satisfying even if you pull it off.
I don't know what else to say other than...meh.