So there was actually quite a bit in this Direct that I'm interested in...and ironically the Smash reveal was probably the one that got me the least-hyped for it.
I'm not saying Kazuya's a bad choice per se (I acknowledge that Tekken is one of the most popular fighting games ever, so it does make sense); it's just that personally I don't really care much for traditional-style fighting games, and hell, I didn't even know what game he was from until the "Smash X Tekken" image appeared.
That being said, from what I gathered from the trailer, he does seem to have some unique abilities that differentiate him from Ryu, Ken, and Terry (in particular him turning into some sort of demon, which was pretty cool on reflection), from what I've inferred, he seems to be another playable villain which is appreciated, and I'm sure he'll be fun to play as when he comes out; it's just that for now, due to my own feelings regarding that particular genre, I'm rather lukewarm towards his inclusion.
I don't hate it, but I'm also not really jumping out of my seat in joy, either.