It's really pretty good - much better than any suggestions that I have seen anywhere else. Ok, there's some stuff that is a bit off the mark (Britney Spears next to Chaka Khan? Really? I do wonder what made them suggest Britney Spears to me), but I'd say that 90-95% is a very good match to what I like, with some things that go a bit beyond my usual taste (but certainly in an interesting direction).
One minor complaint is that it suggests some stuff to me that is in my library. Suggesting "Songs in the Key of Life" by Stevie Wonder is a bit silly when I own it already. Yes, I like Stevie Wonder. Thanks for noticing, Apple. 😉
A major complaint is that some of the playlists are not very well put together. Again, 90-95% is great, but some make me go "Huh?"