Control-wise, it's pretty much the same deal as before. Still no jump button (which is ironic, considering the title of the magazine that features the original series), but otherwise the combat is smooth and as satisfying as ever when you send crowds of enemies flying. Compared with the first game, movement feels more refined and fluid, but that may have been my imagination, and the 40 inch TV I was playing the demo on...
As for new features, a Haki system has been added for combat against Logia-type bosses. (If what I just wrote makes no sense, then you're not a huge fan of One Piece and this game and its predecessor are totally not for you.) There will also be non-canon "what if" scenarios for fans to enjoy. New usable characters are also expected be added. So far, the only definite addition is the lightning man, Eneru, but teasers indicate that Black Beard and Aokiji will be included as well.
All in all, from what's been revealed so far, One Piece: Pirate Warriors 2 feels a bit more like Pirate Warriors 1.5 than a full 2. Then again, the previous game did seem rather abridged, so maybe the first one was 0.75 and this is 1.0?
One Piece: Pirate Warriors 2 will be available on the PS3 and PS Vita on March 20th, 2013.