So I've finished Dressrosa, preliminary opinions.
Story mode wise, it's rather dull up until Marineford (assuming you've played a Pirate Warriors game before, which I have.) You've only got the option of Luffy, Zoro and Sanji for the most part, with Ussop occasionally in it. Ussop, for his part, is absolutely dreadful and takes an age to kill anything. Maybe I hadn't levelled him enough, I dunno. The M3 are much the same as they have been for all these games- haven't used G4 Luffy or NW Sanji yet though. For regular Luffy and Zoro though, I quite enjoy- Zoro's had most of his post skip attacks added to his repertoire and flows quite well.
From Marineford you start getting to play other characters. Whitebeard as I've mentioned is a beast, Ace and Sabo are quite nippy and fun. Franky is the least changed out of everyone I've played- he barely has any aerial attacks so he's still on the ground mostly. Jinbei's still slow as hell. Special mention goes to Law though- they've added in a lot of the moves he had against Doflamingo and it's really fun. Oda should take a look at it for any future fights, it's that good. They've stuck in him using Sterbern by having him open a Room and sending his sword whizzing about. Kid, sadly, seemed quite rubbish. Don't think they knew what to do with him since he's barely fought in the series, so his gimmick is just his attacks occasionally get bigger and it's just quite dull. Bartolomeo I only tried once but I was quite disappointed, his attacks didn't seem given have much oomph. I'll give him more of a try later.
Fujitora, Death, destroyer of worlds, has sadly been nerfed. Still has his big killer attack where he drops everyone into the chasm of hell though.
Played one game with Katakuri and his transformation is pretty awesome, the floating ring donuts appear around him and he gets off about 4 extra attacks at once.
The Vinsmokes are a shambolic decision. Cannot fathom why the designers thought that the four of them deserved to get in- actually, I can. Shared assets for the brothers. They even have some of the same attacks and just scream out laziness on behalf of the producers. Reiju is alright because she's at least a bit different.
Some very weird character choices that take away from the game. They stick a good chunk of the Kyros/Rebecca/Diamente story's in the game in cutscenes, Diamente is a boss, yet neither Kyros or Rebecca or playable or even npcs. There's a few bits like that thoughtoutk but that's been the most egregious so far.
So far I'd say it's fun, but not worth full price. Maybe if it's your first PW game, or like me, your stuck in the house anyway and need something to take up time. And it is a fun game to whittle the hours away. In terms of presentation it's a lot more polished than PW3, but the cut characters and some of the ones they chose to replace them leaves quite a bad taste. But I think when PW5 eventually comes out I'll be waiting to get it on sail. My favourites still PW2.