I've read a handful of books on science/engineering lately and I had recently watched The Theory of Everything and honestly enjoyed it - so I picked this up off my bookshelf and read it too. It was pretty good!
Professor Hawking was an amazing individual and his achievements in theoretical physics are amazing - but he's also really good at presenting advanced topics to those that don't have a PhD in hard science. While I probably do know more about that sorta thing than most people, I'm not well practiced these days but had no trouble at all following along. He tells a good story!
It's not too long or too short really. He does a great job of reducing some pretty complicated topics down to what someone with a basic knowledge of math and physics can comprehend.
It's not a textbook.
I really can't think of much here... I can't really count it against him, but some references to dig in further and see the mathematical rigour behind somethings may have been good - though I may have ignored them all when it was all said and done.
I give this a 4/5 which is pretty solid praise coming from me. If you consider yourself learned (pronounced with 2 distinct syllables here) with an interest in the fundamentals of the universe this is a good place to start.