I've had the 3DS game for awhile, here are my thoughts on it:
Characters:
I have no real problem with the character selection. There's someone for everybody. There's plumbers, Gorillas, time manipulators, swordsman, girls in extremely tight suits, etc. Even Ganondorf is useful in Home Run contest(seriously, I got over 4000 just by using him.). So no problem in the character department.
Stages:
But the stages are not as perfect. Some of them have a huge level of difficulty(looking at you Magicant(Seriously, those birdman helpers are really hard to kill.)). The only few I do like are Battlefield, Final Destination, 3D Land, Golden Plains, Mushroomy Kingdom, Jungle Japes, Gerudo Valley, Spirit Train, Yoshi's Island, Dream Land, Corneria, Prism Tower, Mute City, Arena Ferox, Flat Zone 2, Reset Bomb Forest, WarioWare Inc., Distant Planet, Tortimer Island, Boxing Ring, Gaur Plain, Balloon Fight, Living Room, Find Mii, Tomodachi Life, PictoChat 2, Green Hill Zone, Wily Castle, and PAC-MAZE. Paper Mario, Brinstar, Unova Pokemon League, and Magicant(especially you) are very complicated for me.
Also there is no more stage maker, if you were wondering.
Online:
It's waaaay better than Brawl's, however I experience lag when in a match from time to time. I also like the betting mechanism in spectator mode, really makes you risk things.
Smash Run:
At first it's a bit difficult for me, but then I played a few more and started getting the hang of it. It's actually pretty fun and I recommend it.
Other Modes:
Classic Mode is fun, love All-Star mode. Multi-Man Smash is fun and very challenging(in some of them). Target Blast is a blast. Home-run Contest is a smashing fun time. Custom Miis and fighters are ok, though I'd stick to the originals. And the Vault, oh gawd the trophies are so addicting and dat trophy rush, mmmmmm. So good.
So yeah, I'd recommend buying this.