The western-themed episode found the Doctor, Amy, and Rory in the wild west, where an alien cyborg is holding a town hostage. The episode maintains the rhetoric and vernacular of a traditional western while fusing in a sci-fi twist. The cyborg tracked an alien named Kahler-Jex to a small town where Jex has provided the citizens with electrical and medical advancements. As we learn more about Jex, we find out that he came to the town to seek penance for the atrocities he committed during the war, and the cyborg followed to punish him for his crimes.
Thematically, this fits very well with the post-Time War Doctor. Jex serves as a parallel for the Doctor's conflicted past. This series has had a bit of a darker tone which has left fans uneasy, but I have enjoyed these elements that have pushed the Doctor to be a bit more callous than he has been in the past. My only concern is that they have covered this in the David Tennant specials, and unless this develops into new territory, there is not much need to retread these waters again so soon.
I am still unsure why there was a narrator in this episode. It did not really add anything and almost felt like it was shoved in there at the last minute like Harrison Ford's narration in Blade Runner. Although, if that was the price we had to pay to see the Doctor in a western, it was worth it.