Well this is an interesting idea. It'll be weird because we'll be trying to remember what we thought when first saw/read One Piece but yeah, here goes.
I was wondering if an anime/manga would do well with pirates. I don't really remember much other than that.
I definitely liked Shanks and Nami (anime). I didn't have an opinion on the others except that I hated Helmeppo and I was annoyed by Coby continuing to try and discourage Luffy after the first few times. I also remember liking that Marine who let Coby join the Marines.
I started with the anime and I liked the art and the cartoony feel it gave, it worked well for the show. It was super old though so I just wanted to get to the newer, better looking stuff quickly.
Gold Roger's death, Shanks saving Luffy and Zoro immediately agreeing to go to the Grand Line were cool.
Gold Roger's story and Coby's Grand Line 'explanation' really hyped me for the Grand Line and gave off the sense of adventure and the unknown very well. It was a very good introduction. Other than that, it's not a negative anymore but, at the time I remember thinking that a guy using a third sword in his mouth was pointless and he shouldn't even be able to talk. I don't really remember any serious negatives though.
Meh, I wouldn't do ratings.