Never played Smash or Splatoon online.
Diablo III was fine though. Tetris is as well (lol).
It's 20 bucks here for a year in Germany so honestly: It's a no brainer, no matter how bad it is. Had to pay 5 $ (or more) for a Virtual Console game on previous Nintendo consoles. Having those NES and SNES games alone is worth it.
Not for me actually (using RetroArch in emuNAND) but for those who don't use a CFW I'd say it's worth it.
The netcode might still suck though. Maybe that's why I don't even want to bother with Smash online.