First of all for me a 30min episode seems like more of a special episode rather than a movie.
The story is Luffy's hat goes missing one morning. He has searched all over the ship but can't find it. Usopp has an idea of the thief but no one believes him. So the search begins for Luffy's treasured hat, along the way they run into sea kings, navy and an old man and his friend.
The 3D was a new twist to things but it wasn't my cup of tea. It seemed like they wanted to involve the viewers and make it seem like you were actually there. Most if the action scenes made me feel like I was on a roller coaster. Some fight scenes felt like they were made to be in 3D as you will understand once you watch it.
Overall it wasn't bad, wouldn't mind watching it again but it will have to be 1hr long minimum.