A lot of interlacing threads in this episode although the main theme is that of the discovery of much more about the Gormogon cannibal.
At the same time it reveals more about the relationship of the three Brennans - Max, Russ and Bones - but also about Booth's interaction with them. Yes, Booth has to arrest Russ, but he puts it off till they visit the child in hospital. He also sets up some monitoring of Russ so that his time in jail will be short.
Booth is the heroic action man in this episode - he rescues Bones from the taxi and also the child from the pool thus having to let the bomber escape. As to the Gormogon puzzle, it is Booth who has involved Sweets with the result that Sweets reveals a great deal about the psychology of the Gormogon set up especially the master / apprentice theme which is crucial to the on going saga.
A couple of real horror movie moments - the old man in the nursing home suddenly hissing, and the closing scene when the knifeman springs out of the cupboard - always makes me jump that.