People are asking how much better it is compared to DOA:U?
Well they re-did some of the move lists, so you can't have all the cheeze you mastered in DOA:U and expect it to work with DOA4. Alot of that cheeze is gone, and even if you could still do it you would have to perform it with different button combinations.
Graphics wise the backgrounds are a huge step from DOA:U and are feeling next generation quality. Character models not so much, they are much more crisp, clean, fluid and probably have a few more polys, but overall they did not work overtime on the new character models with the exception of two people characters. Mistress Chief looks like something out of Halo 3. Also Ryu looked even better this time around with his Ninja Gaiden outfit on. I can't wait for NG2.
Countering seems more difficult to pull off, but It's still of the rock/paper/scissors type which can turn off alot of fighting fans. It gives the newbie a chance with a random counter, and the pro the advantage for people who spam the punch or kick buttons/a certain move. Not only is countering more fun, but it deals less damage this time around compared to DOA:U. You can't win simply with counters unless your opponent is extremely predictable.
The core gameplay hasn't changed much either. You still have your wide variety of power moves and quick attacks. A new addition is the "charge up" moves that every character seems to have. Also each character has a few new moves that they didn't get in the previous games. The most major change it seems is the ability to "juggle" other characters. While it was possible in DOA:U it seems far more prevailant this time around, and the computer actually takes advantage of it when it gets the chance.
The online has more variety then DOA:U, but not by a gigantic amount. I forget if DOA:U had tag or not, but DOA4 has that. The lobby system is unique and allows you to watch others fight from a lobby on a TV screen in a animeish setting, but It's nothing to wet yourself about. The online was supposed to be more fluid and less laggy, which it seems to do in most four player or less games, but as soon as you get anymore then that it can be just as bad as DOA:U was.
The only department I think that took a hit is sound. DOA2 had my favorite soundtrack, and that is still the case with DOA4. Some of the voice clips sound new but alot are just recycled.
Ehh... that's about it. if you love the Dead or Alive series you won't be dissapointed by DOA4. If you didn't like DOA:U, chances are you won't like DOA4. If you were on the fence with DOA:U, DOA4 might push you over the fence. If you like fighting games then you'll most likely like DOA4. If your starving for a online fighting game, or fighting game period for the 360... grab DOA4 and you won't regret it. Besides there is little in the way coming for the 360 anyways down the road, the only other 360 fighting titles that come to mind are KOF: Neowave and KOF: Max Impact 2.