I went and saw this tonight, so I thought I would write a bit about it.
Basic info: So One Piece has a live-action show at Universal Studios Japan. The dialog is recorded by the anime cast, though, so the actors simply mime all the dialog.
You have to purchase a separate ticket outside of your park ticket in order to see it. It opened on March 8th and runs for about 80 minutes. It's set in Waterworld section of USJ, so they make use of the stage already present for the normal show that occurs there. Lots of stunts involving the water, fire, boats, and jetskis. You aren't allowed to take pictures or video of the show.
The show also has random song and dance routines.
Basic plot: Luffy daydreams and event in which Boa Hancock and the Kuja Pirates are kidnapped by Disco in order to be sold off as slaves to the Celestial Dragons for Doflamingo.
Basic summary to the best of my ability: The show opens with the post-time skip crew running from the Marines. They are then confronted by Doflamingo who says he will be waiting for them in Dressrosa, taunting Luffy with Ace's Flame-Flame Fruit. Law also makes an appearance telling them they need to get going. Luffy falls asleep.
In Luffy's dream, the crew is back to their pre-timeskip selves, running around and doing nonsensical things. When they exit the stage, Disco appears and receives a call from Doflamingo. Disco needs slaves for Charloss and Shalria, but he can't get any mermaids, and humans just won't do, so he's in quite a tight situation with Doflamingo. Meanwhile, the Kuja Pirates and Hancock show up for some reason. They fight, but end up being captured by Disco. Disco sells them off to the Celestial Dragons. Marguerite gets left behind and is found by the Straw Hats. The crew decides they need to rescue the Amazons.
Duval shows up out of nowhere and helps the crew out. After the Staw Hats battle with Disco's crew, Doflamingo appears and uses his ability to take control of the Staw Hats and make them fight against each other. Brook manages to get away from Doflamingo's control. He later is able to stealthy switch places with Boa, letting her escape from Disco's men.
There's more fighting... The other Straw Hats are able to rescue the remaining Kuja Pirates. Ace appears looking all badass. Doflamingo runs off. Ace and Luffy team up against Disco's crew, destroying the set. The two brothers then say their goodbyes and part ways again.
-short intervene while the pre-time skip crew runs through the crowd and shakes hands/high fives people-
Back to post-time skip, we see Luffy still asleep, and Nami trying to wake him up. A disheveled Disco appears, trying to take Nami as a slave without realizing who she is. Luffy wakes up, scares Disco, and Disco runs off. Law appears telling them they really should be going.
-post-time skip crew runs around high-fiving and themes play to close the show-
Sorry if it's a bit vague... even though it's only been six or seven hours since I saw it, I'm already having trouble remembering things about it.
I was surprised at some of the characters included in the show, though. Never expected to see Duval, but I guess they needed to put those jetskis to work. The costumes were all done entirely well. I was shocked at how amazing Brook, Chopper, and Franky looked. There were at least four different Chopper costumes for his Points and pre/post-time skip.
The park itself is also littered with One Piece foods and goods. Hats were extremely popular. They had hats for Luffy, Ace, Law, and Brook. They also had towels in the design of the Admiral's jackets, and tons of Ace t-shirts.
I ended up only getting a souvenir mug, because the hats were way too expensive for me.