But at least the flashbacks have meaning. They are almost always done to show a character's history and how they got to where they are. A major part of all the crewmember's story is that they are all misfits with pretty grim pasts who did not really have a place they belonged until they found each other.
The flashbacks to eailers events in the series are not nearly as bad other similar series. Naruto has to be the worst at that. I swear that series must have shown the scene where Sakura tries to stop Sasuke from leaving 50+ times and the one where Naruto promises her he will get Sasuke back another 30+ times. There was one time where they flashed back to those two scenes at least 4 episodes in a row and twice in the same episode. That is just annoying.
The 2 min. opening and previous episode recap stuff is one of the ways One Piece has been able to avoid large amounts of filler. It's a trade off and I would rather have a few min. less of show each week but have the majority of it be manga material vs. weeks long filler arcs every other arc.