As a Roman novelist and a historian obsessed with the history of the late Republic and the Principate, I am naturally a huge fan of Hadrian's wall as a place to visit. Some years ago I walked the central part of if (where it goes up more than along) and I wish Wish WISH that I'd had this guide then. In a few years when my son is old enough to do the walk, we will be using this guide.
Bishop is one of the foremost authorities on the wall in particular and the Roman military in general, and his knowledge shows through the guide. Having walked the wall more times than I have had hot dinners, Bishop knows every hummock, ditch and hedge along the way. These two factors combine to make him the perfect guide for the journey, but add to the text an anecdotal manner and a number of interesting and humourous tidbits and you're left with a guide that's a HUGE win.
In fact, for the historically-inclined, it's such a good choice, you can 'armchair archaeology your way along the wall using your kindle and Google Earth.
Brilliant. More than worth the small price. Buy it. Enjoy it. Review it and help spread the word.