Peter Jackson took very few liberties with the story
Erm, perhaps you ought to read the book (again)?
Yes, only a certain amount of time can be used before the film becomes too long, but in places ol' PJ decided that the original plot wasn't good enough, and suddenly Aragorn goes from being a man who has walked the world, taken part in some of the major battles, and approximately 80 years old (and still looking "middle-aged", out of 250 odd years before he died), to being a wayward 20 year old who won't accept his responsibility/destiny. I don't know about you, but I've heard the latter plot idea before!
I have had a conversation with my brother a number of times about the LotR films. We're both major fans of the books, and I think the number of times I've read LotR is around the count of 20. One of us will start the conversation, talking about something or rather in the films, where my brother will say "oh, it wasn't that bad...", conversation goes on a bit... "oh, except that... oh and that, jesus christ! and what about the exorcism Gandalf is apparently performing on Theoden... do these guys have no idea what subtlety is?", and then we have torn the films to pieces on points, not nitpicking, but where perfectly good plot that could have stayed in is removed for dodgy cliche plot. In the books, the idea of Wormtongue being sent to talk Theoden into thinking that he's growing old to the point of losing his grip so that Saruman can do what he likes is a good one. The books go on about how Saruman and Wormtongue were extremely good at what they did with great subtlety. In the films we have an actor is is
bound to be a bad guy to anyone who has seen a single film out of the nearly 200 where Christopher Lee has played a bad guy, and he does it in virtually exactly the same way he always does! There's no explanation why Saruman decided to turn to evil in the films, it's just "because it's Christopher Lee! you know, that bad guy!". And don't forget the line that nearly made me retch in the cinema "you have my sword! my bow! my axe!", Jesus Christ. Who wrote that garbage. Lines from the book are then thrown in randomly like they were quoting some book at random, then they get back to their totally unsubtle and uncreative plot, complete with over-acting and random plot "twists" that end up not being plot twists and just to "spice up the action a bit".
And to people that wonder whether it "could be done", converting LotR properly to the screen, I recommend watching the unfinished animated version, the Bakshi version IIRC it is referred to. That also cuts huge swathes out of the books, but it still lends respect by not screwing with what it leaves in! It has its faults, but it is a far more satisfying watch than the films are.
