Hard work at times, off on a crusade at others, but always worth the effort because there were real insights into a fascinating, if alien, world. The last section was a bit of a rant about the state of modern science, which I didn't really warm to, but the earlier discussion of string theory was top-notch.
Where the book was best was when it tried to nail exactly where modern physics currently is and where it should be going. The sadness (make that anger) Smolin feels at the time currently being wasted by the physics establishment was an eye-opener but not really what I wanted to read about for half a dozen chapters. I was after the nitty-gritty of what the boffins are up to and only got this for half of the book...that half was excellent, however.