I've read through Kingkiller. And, like the rest of the world, am eagerly awaiting The Doors of Stone. That's the last time I'm taken by an unfinished series. :)
I love heists, so the first Mistborn book is my favorite — it's Ocean's Eleven meets fantasy. And, I thought that the whole trilogy (and beyond) was so cleverly pieced together that I re-read it each year. I like that everything has its place, even if it feels a bit too convenient now and then.
His Stormlight Archive series took me two tries to get into, but I'm so happy I did. The characters are well-thought-through, and each book (1,000+ pages) focuses on the backstory of one particular character.
And, I think the more impressive part of it is that almost all of his adult-fantasy books are connected, and that he's setting up a very, very large 36+ book arc that — for now — is only there if you look for it, but with each new book, the ties are coming together more and more.