One Piece does an absolutely amazing job of magnifying empathy through the background stories of its characters. It usually takes several episodes for an arc to be deeply remembered so it is kind of difficult for a 50 minute movie to achieve that same level. Nonetheless, the movie touches upon why One Piece is so great. Luffy is as big of an airhead as ever and Usopp is always spouting cowardly remarks with far fetched and unbelievable lies.
The animation retains the same look with the same level of quality as the first couple seasons. There really isn't anything to complain about, but movies tend to have higher budgets despite it being a spin off movie for an anime, you would expect the quality to be at least better. Still the major battle at the end is pretty good, almost as if half the budget went to that fight. The music and sounds fortunately don't suffer the same circumstances as the animation.
Definitely a treat for all One Piece fans. It doesn't match the magnitude of the show but it does touch upon why One Piece is such a popular show in the first place. It's not an essential watch as the movies' story is completely unrelated to the main plot and none of the characters make a recurring role later on, but if you're a person that wants to make the most out of an anime, this deserves a watch.