It is hard to know where to begin or end with The Chronicles of Thomas Covenant.
I can give some opinions:
Both trilogies involve High Fantasy
Both trilogies have a truly awful Antagonist
Both trilogies have genuine heroes and heroines
Both trilogies feature something truly worth fighting for
Stephen Donaldson is very bright, and it shows in his works
Stephen Donaldson has a lot of insight and experience in certain fields of medicine, psychology, and culture, and it shows in his works
Thomas Covenant is an exercise in frustration.
This is not a person who gets things done. You can kick him in the rear all day, and he won't budge from where he sits.
Thomas Covenant becomes the worst sort of criminal early in the first book of the first trilogy. And you, the Reader, have to live with it.
If you like happy endings, do not look for them here.
Tragedy and angst are as much a part of the story of Thomas Covenant as his leprosy is a part of his life.
In another thread, they are debating paladins.
Thomas Covenant, is the opposite of a paladin.
Thomas Covenant is neutral, if neutrality exists.
Thomas Covenant does not believe in causes, helping people, being courteous, being reasonable, or in anything else I can think of - he does not believe in the existence of the people he is interacting with in the story! (Thus his name, the Unbeliever.)
Linden Avery is featured in the Second Chronicles.
Linden Avery is not a criminal, in the sense that Thomas Covenant is, but Linden Avery is crazy.
That's right. Crazy. Not right in the head. Nevermind she is legally sane, and is a doctor to boot.
How is she crazy? Why did she go crazy? What does her lack of sanity cause to happen in the Second Chronicles? Read them and find out!
Thomas Covenant is a criminal.
Linden Avery is crazy.
And these are the two main Protagonists of the Chronicles.
Prepare yourself for a long, complicated, convoluted, and sometimes appalling ride.