Based on just
Lions of Al-Rassan, I'm really not much of a GGK fan. He had a few stylistic quirks which really bugged me. In my head he's a bit like Spielberg, in that the emotional string-pulling can be way too heavy-handed.
Don't
The Hobbit and
LotR kind of rule each other out? (How stand-alone is stand-alone?)
Same applies to
The Eyre Affair. It's a series if not a serial.
I'm going to provisionally go for
Peace by Gene Wolfe, just so this post isn't entirely negative.
It is a great book, even though it took me two attempts to get started, but it's fantasy in the broad sense (like most Wolfe) not the narrow sense (epic/high fantasy). It's hard to think of standout stand-alone works that are actually epic fantasy. I guess it's not that epic if it ends that quickly.