I'm perhaps in the minority around here as I prefer her more straight singer-songwriter material to the more obtusely artistic and/or heavily jazz-inflected stuff.

Blue is probably a top ten album for me, simply terrific. I offered a lot of thoughts on why in the post that was supposed to focus on the album a few months back, but suffice to say it's a combination of production, instrumentation (esp. the dulcimer out front), and melodies. It's really the only album of hers that I go gaga over, but most of the other ones I either have or have heard are at the very least quite good.