I finally picked up a 360. One of the games I got was DOA4, because I liked DOA2 and DOA3.
I can't say that I'm an expert at DOA4, but I have now played it for many hours, and I have some impressions.
It looks like they were trying to get DOA4 to have a better high-end game than its predecessors: the priorities are a bit more complex and there's a host of new "split second" timing possibilities. They also tightened up the timing on counters and loosened the timing on throws, making the first a bit less dominant and the second a bit more (to the point where you can throw people while they're punching you in the face, which is very irritating to low-level fighters).
They also changed the AI. I find it harder, but that's probably just because I'm used to the old AI. I've always been better against humans. :P
They also weakened the floor game - it used to be that stomping on people and kicking them while they were down was a fun part of the low-skill combat. Although the moves still theoretically exist, they don't seem to be any use even in low-skill combats, which I find irritating. Even if a technique is dominated at higher skill levels, if it is fun for low-level fights, it's a nice ramp. Also, it's a bit easier to get fucked up in a corner, which is interesting at high levels (it's 3D, so keeping your position away from corners is far more possible than in, say, Street Fighter) but, again, irritating at low levels.
They also extended hit ranges a bit, which completely throws off my sense of distance, especially since these hit ranges often extend beyond the fist. That's just bad practice.
The whole game feels a bit more "turbo", which pisses me off. While the speed of a game doesn't affect my ability against other humans much, it makes the AI harder.
Anyway, the end result is that DOA4 is much less accessible than DOA2&3. My office mate tried to pick it up. While he's not an awesome fighting game savant, he did beat Art of Fighting. But DOA4 simply irritated him, because all the low-level play had been sacrificed.
Well, on the upside, there is a massive clarity in which characters have what strengths and weaknesses, and what characters they are strong or weak against. That's fun, and does allow for some level of handicap by carefully choosing a character strong or weak against the enemy.
But why don't they have a handicap proper? Sheesh, it's not hard to program in a damage reduction handicap.