A lot, quite a lot.
Brilliant movies, it's nothing short of a miracle that the book was adapted, not just competently, but consistently so, over three movies, spanning 12 hours in total. It's not something you can really compare to other films, the trilogy is in a league of it's own.
Some themes of the story are more relevant now than they ever were, in today's world.
To any who have not, I'd recommend you read the books, too. It's worth getting into reading for that goal alone.
There is a great talk I found a while back, underrated, some of you may be interested to listen to it.