We haven't played everybody yet, but a few things seem pretty clear. The Tekken system of the buttons corresponding to limbs does not apply at all here. The only thing that seems to be the same as Tekken is the round fixed size arena and the sidestep and throw commands.
We were worried that two-player was going to be somewhat choppy, because of the system having to render two instances of the game but we didn't really feel it.
There are still a lot of other Pokémon in the game as support characters, but we don't have all of them unlocked yet, so maybe we will have to save that for another time. I'm sure that we will discover even more about the game after playing it for a while.
Also - there's a Splatoon Splatfest today, so if you're not busy playing Pokkén, get out there and ink some stuff! (Don't let my older son catch you standing around at the spawn AFK, either!)