Overall one of the best manga's ever and I've read a lot of manga's. I rate it way higher than Bleach.
The anime is also quite different than most other anime's considering Oda is closely involved in it. The amount of fillers compared to the amount of episodes is also quite low compared to other anime.
Both in the manga and anime the start might seem not great because the artwork seems odd and the story a bit lame, however you just need to get to the Barati/Arlong arc. From that point you just can't stop anymore, especially when they go into the Grand Line as then the story really goes smooth. In the anime though the added a filling arc about dragons in it just before they go into the Grand Line. It's the same as in Bleach. When I first started watching Bleach it just seemed stupid. I found it easier to watch the start of OP than Bleach.
The artwork also evolves. At the start it might seem childish, however OP now counts 630 chapters. There's no mangaka who's going to claim that his style remained exactly the same during such long period. IMO Oda is one of the best artists considering he can clearly make all his characters look unique, while with a lot of mangaka's their characters often look so much alike it's difficult to keep them apart, and he's incredibly detailed. When you read it, it feels like Oda planned everything from the start xd
He also succeeded in one of the most difficult things and that's having a power gauge for all the characters that's not contradictory, which is for instance in Bleach and DBZ a big problem as their power gauge is quite messed up.
One Piece is extremely funny, has lots of action, gives for a lot of characters a background even minor ones, the girls are hot <3 and the amount of adrenaline you boost is ridiculous. Oda can even do stuff, for which you would normally curse a mangaka for all eternity, and make it acceptable for you.
