To be honest, I always associated Bill Bryson with light travel books, so I was pleasantly suprised to find his refreshing writing style applied to etymology; not always the easiest topic to entertain with!
Having said that, there is so much more than etymology. The anecdotes are amusing, and you will find yourself repeating them to everyone you know. The work that debunks urban myths is fascinating and, as is often the case, fact is stranger than fiction; some of the truths behind words and phrases are truly special.
The lists of when words were first used did not appeal to me personally, although I am perfectly willing to believe that there are people out there who would be interested, but they are fairly easy to skip.
The one thing I take away from this book more than anything else is respect for American English. As a young Englishman, I have been pre-conditioned into a certain disregard for 'Americanisms'. Yet after reading this book, you will see how useful many of these words are, and the ones we choose to attack are very limited. I think the book is worth reading for this information alone.
In conclusion, a good read that you can take your time over.