I could never get into The Chronicles Of Thomas Covenant the Unbeliever, but I know a lot of people who really enjoyed them.
I'm an insanely finicky reader. So, when I say I gave the first book to this series a try? Don't give it too much weight. I give up on books far too easily and if I remember correctly, I gave up after the first two chapters. Extremely rare when that I will return to books I have tried and failed to finish ... like Catch 22. So rare, I can only say it happened once and as of last week where I finally started and finished the economics and physics heavy Accelerando by Charles Stross (which I previously attempted to start and read at least 4 other times).
Another poster was waxing lyrical about Zelazny’s Amber series.
I've only read his standalone Lord of Light novel. Fondly remembered at a vague rate.
Some of Terry Pratchett’s stuff has been televised, The Hogfather, The Colour Of Magic and Going Postal.
Super waaaaaaaaaaaaaaay too intimidating to start a series of books as long (and costly) as the 41 novel Discworld series. Though, I suppose they're not too intellectually challenging a read. Being humorous helps. Still? I can't see myself pulling that trigger anytime soon.