The Great Book of Amber - Roger Zelazny I was still new to fantasy, having been a hardcore horror and sci-fi fan, then going through all of Zelazny's other works, when I decided to sit down to these stories.
Seriously, I was impressed with the easy progression into a multi-universe view delineated between ultimate order and ultimate chaos. Gorgeous magic system where you follow mandalas, epic battles, and the almost requisite tripe of amnesia. (Oh, sorry, i meant trope.) I loved the first 5 books better than the second 5, but Merlin's story did have a more epic feel, in my opinion.
It's still hard to find fantasy as good as what he wrote, although I'm still willing to keep looking. :)