So, OP is on a month long hiatus. I think it'll probably skip right ahead 2 years later without showing the specifics of the training that the SH crew until they unveil they're brand new techniques.
If I had to give OP a single flaw, it would have to be that its build up and pacing can be rather slow (Skypeia, IMHO the worst arc, was way too long), Oda himself has acknowleged this by commenting that he had to cut out parts of the Enies Lobby arc since it was too long (namely a greater expansion of Lucci's past), but I think Oda is improving on that as well, Thriller Bark quickly stepped into high gear, the same can be said for the Sabaody arc, and the Impel Down arc could only be called frenetic in its insane pace.
Not only that, OP isn't as bad with pacing as other series are *coughberserkcoughreborncough*. Although I will admit that the earlier arcs don't match up to the later ones (The Baratie arc being the second worst arc of the series, plus Don Krieg wasn't nearly as awesome as Kuro or Eneru were).
One Piece is good because of how well thought out the plot is. It can be very silly but when it comes down to it, it can be very intelligent and the world is both very consistent and believable. It is unabashedly shonen and takes pride in both the silly and serious aspects of it.
Off topic but,
Originally Posted by Innis Cabal
Really? Tell that to Double Arts.
I'm so glad I'm not the only one who still remembers Double Arts.