I can only speak from my experience in reading the manga, really. I assume the anime falls into the same general patterns, not accounting for filler and padding.
Honestly, I had to force myself through One Piece, not really because it is bad per se, but because my enjoyment of its individual arcs seems ridiculously inconsistent.
I remember feeling bored to tears by the early series, at least until it reached the part where they recruit Sanji. That part of the arc was pretty cool. The Grand Line should be where things really pick up, but frankly, the Drum Island, Alabasta, and (dear God Almighty) the Davy Back segment all bored me to tears. But none of those can compare to the nightmare that was the Skypeia arc. I was so jaded by then that I didn't even make it to the Enies Lobby arc... which is supposed to be great.
Instead, I skipped ahead to Impel Down, which I actually enjoyed. And then the timeskip hit and we were faced with the Fishman Island arc which... I have mixed feelings about.