I'll begin by saying I've never really understood why people call Dead or Alive a button-masher. Sure, you can do powerful comboes by just mashing a button, but the well-designed counter system means that scrubs will get mauled by a decent player any day of the week. Similarly, experts will be able to avoid their opponent's counters by mixing up their attacks. I always found the DoA combat system great; enough depth, plenty of fun, lots of style.
DoA3 improves on past incarnations with, of course, superb graphics. Superb doesn't quite cut it, of course; they're just breathtaking. In addition, there are pretty CG movies as well... It's been a while since the last time we got nifty CGI for each character (not since Tekken 3, I think).
Four-player tag matches ensure plenty of replayer value, but there are scant other extras. Only a handful of extra costumes (more with the booster disk, of course) and a hidden character.
If you like fighting games, give DoA a try. If you like its combat system, you'll be getting tons of mileage out of this game. Highly recommended.