Wholesale changes for the better, but wholesale changes nonetheless.
1) Dead or Alive 4 had little to no strikes - let alone guard breaks - that were actually safe on block, let alone allowed significant frame advantage to catch opponents who mash out of stun unawares. This ultimately led to throw punishment being the most effective way of dealing guaranteed damage making the game more defensive and slower paced in higher levels of play. Dead or Alive 5 fixed this by allowing guard breaks and some strikes to become safe (and even neutral) on block, balancing DOA5 out to be just as rewarding for playing offensively as well as defensively.
2) Dead or Alive 4 had universal offensive holds. In theory, it would sound great at first because everyone has a command throw that goes through attacks. But combined with having every move track, the meta was exactly the same for the entire cast to deal damage, and whatever individuality that strikers and grapplers had was lost with this universal mechanic. Dead or Alive 5 not only fixed this by having only some moves track the opponent, they gave the offensive hold mechanic to all the grapplers, Leifang, and Hayabusa.
3) Dead or Alive 4 - at least after the 4.1 patch - removed all unholdable stuns, which would've opened guaranteed situations for non-grappler characters. Furthermore, you could even hold from a wall splat. The reason these were bad design choices competitively was for one reason: It defeats the purpose of the defender trying to avoid being put in such a dangerous position in the first place, and does little to award the aggressor for putting them in that dangerous position. The defender could simply hold without fear of being jeopardized for guessing too much out of stun, and without unholdable stuns to set up, the aggressor still has to fear having the offensive pressure lost through one lucky hold. Dead or Alive 5 balanced this out by not only adding several types of unholdable stuns, but making it impossible to use holds from a wall splat since your body won't be touching the ground, rewarding the aggressor for putting the opponent in that position. Of course, the defender could still hold out of some stuns, but they have limited times to guess depending on the setup.
Before you make assumptions about me and my intentions here, I am in no way, shape, or form saying that DOA4 was not a fun game to play, and I'm not "trashing" the people who still enjoy it. For me, this was the first DOA game I truly started leveling up at with the competitive community, and I had my share of friendships made along the way. I have lots of fond memories of it during that time, and I'll admit I have a little fun going back to it from time to time for nostalgia's sake.
Furthermore, I'll go so far to admit that like some who defend this game to the death to this day, I too thought the game had no flaws on a competitive level. But as DOA5 came along and I was shown DOA4's flaws compared to 5, it gradually started to make more sense why - despite its big push in CGS and one-time showing at Evo - it was a flawed competitive 3D fighting game. I was proven wrong, and I felt compelled to at least try to share my flawed perception of the game then compared to now through this post. It also didn't help that throughout DOA4's entire lifespan, it has only received one patch, and it worsened the game's competitive nature as opposed to improving it. DOA5, in comparison, had far more support from Team Ninja to address and even balance the game further, especially with the inclusion of new DLC characters.
If there is one thing I can say I preferred to DOA4 competitively compared to 5, it was its use of the ground game. It was consistent, and easy to understand across the board: If the opponent doesn't techroll, it's a free 2k, and a second low attack of your choosing to force the opponent up in a specific position. THIS is the ground game I would personally love to see come back. Also, tag was more balanced here than in DOA5, as the gravity in tag was unchanged from the singles format. However, these the only good things I can say about DOA4 competitively.
All things considered, Dead or Alive 5 is not a broken game, no. If anything, it was the game that broke the shackles that were holding back DOA4 competitively. However, I still believe DOA4 is still a fun game to play in its own right, and if that's what you prefer to play, you do you. I'm not here to judge anyone's tastes, only provide understanding of why competitive players don't think highly of DOA4 as a competitive game compared to 5.
More of this Awesmic and less of the "victim" Awesmic please!