The Dark Crystal is an absolute favorite of mine 'now'. When I was a kid (I was 9 when my dad rented it for myself and my sister to watch, this being back in 1988), I didn't really care for it. Maybe because it was just a departure from what I knew of Henson's work prior to it.
I saw it again in 1993, and 'then' it grew on me, but never thought to buy myself a copy until its DVD release.
There were plans of a 'prequel' film, but they sadly fell through. That would have been a fun watch......or a horrible mis-step. We'll never know.
Those two animated Tolkien movies (The Hobbit and Return of the King were commissioned out to Topcraft, which eventually folded into Studio Ghibli when most of its former team was hired on by Miyazaki and Isao Takahata. They did some work on Miyazaki's film Nausicaa of the Valley of the Wind. They worked on that movie The Last Unicorn as well. A pretty busy studio in those days.
Ralph Bakshi's take of LotR didn't do it either. It's more of a 'technical' movie. It took out too much of the story in trying to compress two books down into 1 1/2 hours.
Didn't care for them too much as I was engrossed into the actual books (this was in the early '90s when I saw those movies) at the time. Loved the live-action adaptions though. Those would not have been doable in the 1980s or even the early '90s. So much CG work, but thanks to the advancements of the technology, you can barely tell unless your eyesight is better than 'perfect'.