Yeah, TTT is by far my least favourite of the films. The first 45 minutes or so are badly edited - so many running shots! There's no sense of drama or urgency in the Three Hunters sequence, just way too many wide-angles cut awkwardly with bad dwarf humour.
Then there's the Aragorn-Warg-cliff incident, which really gets my goat. It's not like Tolkien's text is lacking in fake deaths - there's Pippin ("and his thought fled far away and his eyes knew no more", or however it goes), Frodo with Shelob, Gandalf... probably more I'm missing. :p And the dream scene with Liv really irked me... mostly because Liv does. I liked the prophecy scene despite her, simply because it was very Tolkien and very beautifully shot, but I'd still have been happier if she weren't in it. :p
What else? One too many Gollum/Smeagol dialogues, diminishing the impact of all of them; that awful political speech Sam made; too much Frodo falling backwards; the butchering of Faramir's character into a shifty-eyed sleazebag; eugh. I could go on. Oh, and Gandalf's return was handled very clunkily. So was Treebeard, although darned if I know how one would translate that to film un-clunkily.
Basically, I liked a few things about the movie - Eowyn, Wormtongue, the feeling of tension before Helm's Deep, some of the Helm's Deep battle (and for some reason, the Elves showing up didn't really bug me) and some of the humour. But I really think it's the weak link. Even the music, which I think is some of the best music to be written in the last fifty years or so, period - in this film it comes across in quite an obvious, John-Williams-leit-motif-type way. "Oh, here's Rohan, blare out the Rohan theme" - you know? The whole thing just didn't seem as true to the spirit of Tolkien, and the film had neither the purity of Fellowship nor the emotional catharsis of ROTK. When I saw it for the first time, after a year of extreme anticipation, it left me with a slightly sour taste in my mouth; and made me nervous for the entire next year that ROTK wasn't going to be good. (OK, maybe I took the whole thing a tad seriously... I was writing a diary in Tengwar at one point!)
ETA: Forgot to say that while I am looking forward to The Hobbit, I'm skeptical. I didn't like how dark the trailer was, and how overtly it seemed to be tying the film in to LOTR. The start of Fellowship had some delightfully cheery, hobbity, folksy moments, and I hoped for more of those in The Hobbit, not less. I hope he doesn't skew the tone of the story just to make it more LOTR-ish; you know? Or simply because he's Peter Jackson and likes being macabre.
Must say, though, I'm deeply impressed that eleven, twelve years after starting filming for LOTR, Elijah Wood can believably play a younger Frodo than depicted in LOTR. He really has a (creepily?) ageless face. Hard to believe he was only 18 when he started filming LOTR! I was never hugely impressed with his performance as Frodo - I was more struck by Aragorn, Boromir and the other hobbits - until I watched all three EEs in a row one time, in the DVD lounge of a cute little theatre. (Quite the marathon!) When viewed in an arc, his performance really is impressive - especially given that they filmed out of sequence and over the course of, what? 18 months plus reshoots? The difference between the Frodo at Bilbo's party and the Frodo who looks up at Sam from the cliff at Mount Doom with that heartbreaking "please just let me die" expression... it really struck me for the first time. Hard role to pull off... kudos to him and all that.