Plot: Nice touch to include all those mythical creatures and monsters, the location really helps the story and makes it worth for watching for a good amount of time. Kind of makes a connection between Acneint Story and the Middle Age in a phantasy-kind-of-realistic way.
Characters and Cast: Imo, it couldn't have been better. Each actor makes the character and gives them a personality to them that fits correctly into the story. Aragorn and Legolas are my favorites way far than anyother character. The ones that could have needed a touch or two were the hobbits Merry and Pippin, yet they seem to make worthy the story. The villains are also quite interesting and manage to oppose their hero counterparts.
I liked quite a lot the trilogy, specially everyone's favorite phrase: "My precious!". If the movies would be filmed again, nothing they could add or edit would make them better than the originals.