First off, Donaldson was severely handicapped by his poor writing skills with Lord Foul’s Bane. His plotting, pacing, and other skills improved in later books, but in LFB they were pants.
I firmly believe that in great part the virulent reaction against the Covenant books is because Donaldson specifically intended to deconstruct the fantasy genre based on Lord of the Rings. The Land is set-up to be the perfect fantasy world that needs a hero to save it – and Thomas Covenant is set-up as a slap in the face to the reader who wants to insert him/herself as that hero saving the Land.
As you read through the books, the depiction of the Land is there to lure in fantasy readers whose own fantasy would be to actually wake up in their fantasy world as some fated hero. And Covenant is there, obnoxiously throwing back in their face how foolish such a fantasy is. It’s no coincidence that he’s got a ring like Lord of the Rings has a ring; it’s a deliberate evocation of the LotR genre.
Covenant’s leprosy, VSE, and obnoxious personality are absolutely necessary for what Donaldson is trying to carry off. Without the real threat of backsliding in his vigilence against his leprosy, Covenant has no rationale that the reader will accept for his continued Unbelief. The reader wants Covenant to believe in the Land, because the Land is written so that is what the reader would want. This is why Covenant keeps telling parables about leprosy – so that the reader is forced to confront what could happen to Covenant if he gives in, and believes, even a little bit.
That said, I don’t think that Covenant’s Unbelief is handled consistently through the first trilogy – and is dropped completely by the second. Donaldson had a good idea in dropping Gildenfire out of the narrative. But I think that the inclusion of Hile Troy does serious damage to the question of whether the Land is all a delusion in Covenant’s head.
I’ve found, in discussing Covenant, that people have a hard time getting past the “he’s not a hero!” issue. Even referring to him as the “protagonist” doesn’t help. He’s the point-of-view character, but it seems that most people can’t get past Covenant’s obnoxious personality, and his actions (e.g., the rape scene). At the same time, they’re usually fond of the heroes-cast-as-heroes characters: Lord Mhoram, Saltheart, Bannor. They just don’t like feeling that Donaldson is trying to force them to sympathize with the unsympathetic Covenant – probably because they recognize that Covenant is being written to rip apart the reader’s own fantasy.
The thing is, in the end, that Covenant does turn out to be a heroic protagonist. It’s a redemption story, and Covenant not only ends up doing the right thing, but ends up doing it just like Frodo would – by stupidly going to the heart of his supernaturally powerful enemy’s stronghold, with almost no hope of survival or success.
At the end of a deconstruction and criticism of fantasy novels, Donaldson yanks the rug out and makes the point that the important thing about fantasies isn’t that you believe in their validity – but that you accept their validity as much as the validity of the real world. After kicking the fantasy genre in the teeth through three books, Donaldson turns out to be a softie.