I watched The Last Valley yesterday and did a little background reading online. I'd like something that's somewhat comprehensive if possible, but I know that may be asking a lot.
You probably can't go far wrong with Peter Wilson's Europe's Tragedy. It's a solid one-volume introduction to the conflict, providing an overview of the course of the war, its many actors and various factors.
The problem of course is in the word 'comprehensive'. Wilson's is not a small book but it still can only touch on the key aspects of what is three plus decades of history. I'd recommend it as a starting point, though.