Being that these are so short, there isn't really much to talk about storywise. Does it follow any path of Movie Z? No, it's just it's own thing. We catch up with the Straw Hats as they are lounging around on the ship, enjoying the sun, getting a nice little bit of rest and relaxation. We do surprisingly get a brief battle thrown in for good measure, but it's only there for sake of comedy. It was still a nice addition though. The rest of the special just includes the cast talking among eachother, to random gags. Nothing special, but it will left me with a smile on my face. I did find one thing a bit odd about this whole thing though. Despite this having the phrase "Glorious Island" in the title, the whole thing takes place on the ship. Aside from maybe a brief daydream by Luffy. Might be a nitpick, but thought I should still mention that.
Now there is one thing I feel I should definitely talk about regarding the content. For something so short there is actually a pretty hefty amount of fan service thrown into the mix (chests, butts everything). And yes it seems as One Piece progresses we have been seeing more and more of it. However, it's REALLY apparent here, which is either a positive or negative depending on how you like your One Piece.
The animation really stands out. We get so many beautiful splashes and variety of colors in this, it's really appealing to the eye. If you can find these specials in HD, I highly recommend doing so.
Sound is good as well, though it's reused from the show, so there isn't anything new here.
Despite the fact that these specials are only about 5 minutes long, I was surprised to see just how well each of the characters held up. They all retained their personalities and quirks we've come to know and love. So much so that I would say that even if someone has never seen One Piece, it would still give you a great idea of what each character is about. Not something very easy to do for such a short amount of screen time.
So is "One Piece: Glorious Island" deep and a must watch? No not really, but taken as the short special it was made to be, it kept me entertained. The heavy fan service moments may annoy some viewers, so it's not a special I can recommend to everyone. However if you're looking for a small burst of One Piece antics, there is enough to enjoy here. Sometimes it's nice to see what our heroes love to do when they are not saving the day...and that's having fun!
