i'll make it quick:
Movie 1: wasen't interested, didn't watch. I prefer the more rounded cast of strawhats
Movie 2: fun time. Slick animation. Quick, to the point to set up fights and conclude. Funny as hell too.
Movie 3: too much Mobamby, hated him. Chopper was great, same style of fight set-ups as movie 2. Less funny. Don't really watch it as much.
Movie 4: Great time. Hated the kid and old grandpa… waay too much screen time. Other than that, the setting and plot really fit a pirate-like atmosphere. The bar-fights were great, and Shura didn't suck. Gasparde got his ass beat. Sanji figuring out his weakness was a nice touch. Good balancing of cast.
Movie 5: Plot and story was really really boring. Past promises with characters important enough to Zoro, to jeopardize his relationship with the crew was bullshit. End fight was cool. Luffy's line at the climax was awesome though "ZORO! I will become the pirate king and you'll be the world's greatest swordsman!! THERE IS NOTHING YOU CAN'T CUT!! YOU CAN CUT APART THE MOON!" (or something to that extent, I watched a bootleg).
Movie 6: My favorite. Not only does it balance the cast NEARLY perfectly throughout the film (except for Luffy taking over the end), but it really brings out each character's personality. Luffy literally steals almost every scene in this one, but each character has their own moments to shine (Usopp's lies, Sanji's cooking scene, Zoro on the boat chase, Chopper in the graveyard, Nami drinking and keeping Luffy in line, Robin always observant, yet never impeding). The plot is also balanced, with a simple, yet interesting mystery, action (sure not many "fights" per say, but the straw-hats make much use of their talents), and even a little horror. Movie 6 IMO has just the most diversity packed in it out of the other OP films. I could care less what other's think of the animation, I find it to be great in this one. Sure it's not that detailed, but it FLOWS. There is soo much more liveliness to the character's movements that you really get a great sense for their personalities if it's your first OP experience. Which by the way, for any of my friends who are interested in One Piece, yet don't want to invest time into the actual show, I always start them with this movie. They are usually hooked afterwards. Oh and did I mention, this one is funny as hell?
Movie 7: BOOBS? Had to get used to that one. Animation was very well done. Lively and fun. Kinda general as far as things went. I enjoyed that there was no super powered bad guy in this (unlike movie 5...), and Luffy simply whooped him. I suppose for me the most enjoyable part was the character interaction in the very beginning on the lifeboat.
Movie 8: Good movie... if you haven't seen the Alabasta arc. Kinda pointless, but still good.
Movie 9: saw it recently. Wonderful! I had no subs, but I really didn't need them. The what if....? changes were fine with me (although the beginning, seeing all the crew on the Sunny without Chopper there just felt WRONG!). Leaving out the chessmarimo fight for the Luffy Mushal battle was a mixed bag for me... i mean, it IS chopper's movie, why take out his battle? But the replacement battle was just sick!! The animation from movie 6 was taken to the extreme!! Very good in all! (I want Skypiea next! or east blue perhaps?)
Movie 10: one word.... BROOKE!! I'm sold, looks killer!
well there yah go, hmmm.. i guess it wasn't so quick after all?