I think the theatrical cuts of Fellowship and Towers are fine, but the theatrical cut of Return is terrible for me personally. They completely cut the romance between Eowyn and Faramir, so all you see is her heart getting broken by Aragorn, her uncle dying to the Witch King, her killing the Witch King, and then nothing, that's the last you see of her in the movie pretty much, no happy ending for her, just the sadness of losing the man she loved and her uncle in the span of about a week. Extended cut brings back those essential Eowyn/Faramir romance scenes to give her a happy ending.
They cut some important exposition about Aragorn in Two Towers, about his Numenorian heritage. They also cut the encounter of Gandalf and the Witch King out... although in the film it took place on the way to the Citadel and in the book it was at the front gate. With Fellowship, I agree with Curl, while those bits fit importantly in with the psychology of the books, in the much more simplistic snapshot of the story the films give, they don't really fit.
That aside, I found the theatrical version of Two Towers had poor pacing compared to the extended edition. It feels much more like he cut up what was otherwise an excellent film as far as blockbusters go and instead made something clearly inferior to the Fellowship of the Ring the year before. I think the Extended edition did a lot more to fix the story, especially for the people who had never read the books - I always found it weird why someone would want to see the film Lord of the Rings without reading the books... It's kind of like wanting to read a book about a Star Wars film without watching the film, except reverse.
I describe myself as a little dose of toxic masculinity.