Quite a few, in fact. Here are the first that come to my mind :
- No more critical finish. More or less replaced by Critical Edge, special moves that drain the Soul Gauge. Among which...
- Guard impact is now a special. Performed through 4A+B+K, it will consume half a level of Soul Gauge.
- Character customization has been decoupled from the game mechanics : Equipment no longer alters the character's stats. If you come across a guy in a silly costume, it's of his own will, not because he tried to max out Defense and HP.
- Faster gameplay. Versus time limit can no longer be disabled. The maximum time that can be set is 60 seconds. Time Out should be a rare occurence nevertheless as most move sets have been drastically sped up, with attacks being sensibly more powerful than before.
- Movesets revisited. Ivy's stances have been removed, Natsu, while a spiritual successor to Taki, plays differently... Everyone is faster, as I said before, and there's the addition of the Brave Edge moves.