I'm also reading Rebus in order and agree this was not quite up to Rankins usual speed. Perhaps it's the passage of time made the politics a bit trying and difficult to revisit. Rebus remains an irascible old sod and the alcohol is catching up to him, but he still has one or two friends on the force and eventually the puzzle is resolved. You need to read it to watch Rebus continue to develop.
Great book but the end was a little predictable in saying that I am reading the Rebus series in order (with others in between) and think that Rankins writing becomes recognised. So for someone who has gone a decent time between books or hasn't read Rebus before it's great.