I've played a couple of solo sessions and really enjoyed them! Sparks are so cool -- they make it really easy to "zoom in" on parts of the game that you want to give more attention and complexity. Sigils are also great! Very convenient for solo play. 

The book itself is excellent. The art is gorgeous and fun, the layout is very clear and organized. I love how many examples of sparks, characters, etc. are in the book.