Some parts of the anime were not that great, I agree. The dragging out of Enies Lobby and some of the padding in the Davy Back Fight serve as perfect examples of where the anime isn't that good, and the animation quality can be pretty variable as well. Some of the filler, like the Warship Island arc, the Goat Island arc and even the latest Ice Pirates arc, were also pretty damn shitty, in my opinion. But some of the filler is genuinely enjoyable or even good, like the Rainbow Mist arc and most notably the G8 arc, the latter of which I honestly loved. Even a friend of mine who is not into One Piece at all was impressed by the few episodes of the Rainbow Mist arc he saw, and was surprised to find out that it was filler.
But other than that, I don't see anything wrong with the anime. The animation is decent, far better than some other long running television animation out there, the voice acting is perfect and the music is amazing. I can totally understand preferring the manga to the anime, but condemning the entire anime as shit is something that I personally don't get.