Series which I love:
Roger Zelazny's Chronicles of Amber
Steven Erikson's Malazan Book of the Fallen (haven't seen Esslemont's work yet)
Jim Butcher's Dresden Files and Codex Alera
Dan Abnett's Inquisition works and Gaunt's Ghosts
Patrick O'Brien's Aubrey and Maturin (aka Master & Commander)
Raymond E Feist & Janny Wurts's Empire Trilogy
Douglas Adams's Hitchhiker's Guide to the Galaxy
Steven Brust's Taltos Cycle
Lois McMaster Bujold's Curse of Chalion and Miles Vorkosigan
Just about anything by Michael Stackpole
Series which I find tolerable but not vital:
George RR Martin's Song of Ice and Fire
Eric Flint et. al.'s 1632 (though this is slipping down, the further the books go)
Raymond E Feist's Midkemia work in general (very strong start, but significant quality dip as the series wears on, with one or two happy exceptions)
Terry Pratchett's Discworld (They're very good, but I overloaded on them and am now somewhat averse)
Series which I dislike:
Terry Brooks's Shannara
Terry Goodkind's Sword of Truth
JK Rowling's Harry Potter
Robert Jordan's Wheel of Time
David Weber's Honor Harrington (though I liked the first few books, it went waaaaaay downhill)
If you like some of the books in my "dislike" column, I'm not saying that "You're doing it wrong" or any such - merely that they don't click with me, for varying reasons. If you're happy with 'em, then good on you!

(@Biblioholic: I enjoyed the first Dune immensely -the others, not so much- and I'm a fan of Borges and Garcia Marquez as well)