I purchased the LPG Middle East before traveling to Kuwait to work for 6 months. I found the content fairly well prepared me for what to expect, and hence I managed to survive my time there.
I thoroughly recommend buying the Bahrain, Qatar and Kuwait guide in conjunction with this book as the Middle East guide does not contain much information about these countries. Also, if you are not planning on traveling to many countries in the Middle East, you may want to look into a smaller book as the Middle East guide is thick and heavy. The Kuwait, Qatar, Bahrain guide is 1/5 of the size - much more maneagable for backpacking with.
The Middle East guide is useful for information on visas etc..and provides loads of contact information for planning your travel. One of the most useful parts of the book was the back section on language and ettiquette. As a single female traveling to these parts I was appreciative to have some guidance in this area.
The Lonely Planet - Middle East is not 100% comprehensive, but is the most up to date source of information on the market - and is set out in an easy to follow format. Some of the restaurants recommended were definitely not the best. I even wondered some of the time if the reviewer went into them to eat?! (For eating in Kuwait, you HAVE to go to Greenlands Vegetarian Indian house in the inner city. Also, Alganims on the Gulf Road - these places are 5 star+++, but very cheap!).