The Doctor and crew arrive in a frontier town under siege by a deranged mechanoid, hell bent on exacting his revenge against an alien with a Mike Tyson tattoo, he will have his vengeance no matter how many precious adorable bulgy eyed children live there.
There is a pretty good moral conflict, dampened a little by the road sign dialogue. "Hurrr, you're guilty like me!, It would be easier if I were just the mad scientist!".
It was ok, but not great. It pretty much told us what we already knew - The Doctor was a cunt at the end of the Time War and is like that war criminal over there and he feels just awful about it. Probably wanted to make sure we remembered that before the War Doctor came along. Probably going to be the last of that theme we see, thank god.
And hey, John Crichton was in it.