Any long tedious series worth reading?

I've stayed away from most series that go on indefinitely, but are there any worth trudging through?  This includes licensed drivel such as D&D, Battletech, Shadowrun, MTG, Battlemage, Warhammer, Dr Who, Xena, Buffy, Marvel or DC based novels, Star Trek, Star Wars, and any series which exists to promote future sequels (including Harry Potter, Wheel of Time, etc).

Tad Williams "Otherland" series is very good... uses a setting similar to William Gibson's stories.  His fantasy-based series is also pretty good.  They're both 5 books each, I think?