How about 3 epic films that convey the vast majority of the challenging books that they are based on?
The thing of it is, watch them again, what exactly about them made them hard to make? Some camera trickery with little/big people.... wow, cinema has been doing that for 50 years. CGI for all the impressive castles and the like.... completely new tech... not so much.
There really isn't anything at all about LOTR that makes it difficult to portray on films, its an epic tale in length, but thats it, its fantasy/cgi/quite simple shots in the most part. I mean, half its its cgi infront of green screens, half of it is a small group of guys walking a lot, its not exactly unfilmable.
When I first saw them, epic, I did love the films. I'm not sure if its the number of times I've seen them, or being older but they are getting more irritating.
Without wanting to come across un PC, all the singing in elvish bits, are just gay. In a book they can come across sincere and nothing wrong with them, in the films they are all painful to sit through. There is a lot of over acting and a lot of really badly done scenes. Almost the entire wraith king crap was poor, poor CGI, really badly acted scenes. The Elrond brings the sword and whips it out with painfully cliched music score and stupid zooming in Michael Bay esque filming.
Every time I watch them there is some new scene that I realise is actually pretty bad. They are still great films but for the time and money spent I think they could be significantly better. Largely because the "bad" scenes are both stick out like a sore thumb, the Elrond scene in particular looks like something a studio insisted was thrown in, it felt completely out of place, suddenly like a disney film with the music and filming style to convey the sword is really special. But most of the bad scenes were so obviously bad that how were they done like that in the first place.
Meh, its nitpicky, the films overall are great, just not as good as they should be, and they are a country mile ahead of most of the other absolute turgid crap that gets made that its flaws are VERY minor in comparison.
I really dislike the "hard to film" crap that gets spouted about it, great and insanely detailed/descriptive books with a fantastic story if anything make a film far far EASIER to make.