These are what we call the 'YMMV items.' Things that some people find in this work. We call them 'your mileage might vary' because not everyone sees these things in the same way. This starts discussions in the trope lists, a thing we don't want. Please use the discussion page if you'd like to discuss any of these items.
YMMV: The Mists of Avalon
Anvilicious: Religious extremism and intolerance are bad, inclusive spirituality and freedom of religion are good.
Les Yay: Morgaine with half the women she encounters
Morgaine and Raven (it's implied that these two actually do have some sort of physical relationship)
Narm: At one point Morgaine laments the fact that all the men she's fallen in love with have been closely related to her. It's meant to be sad, but comes off less as "Fate has treated me cruelly" and more as "Why can't I stop falling in love with my relatives?"
Seinfeld Is Unfunny: In regards to feminist treatment of the Arthurian legend. Nowadays, there are a fair amount of retellings from a female perspective (such as Gwenhwyfar and I am Morgan Le Fay), many of which take a less heavy-handed approach than The Mists of Avalon. It's easy to forget how groundbreaking TMoA was, in spite of its flaws.
Squick: In the book, while Morgaine is preparing to greet the Horned King, she Sees that the little girl who scattered blood on the fields is being raped by a sinewy old hunter. And Morgaine is apparently cool with this? Oh, and about a page later she realizes she's had sex with her own brother.
Lampshaded when Nimue needs to pass water and is afraid to do it in public. Morgaine is puzzled as to why would anyone want to spy on someone passing water.