A Town Called Mercy - spoiler-free round-up

As with the last couple of weeks, bits and pieces of a non-spoilery nature I've picked up from here and there. Must admit, there isn't quite so much out there on this episode.

The Doctor's four-legged friend - telepathic, and called Susan.
There are 2 time-travelling Doctors.
Our Doctor gets mistaken for someone else - that other Doctor?
He likes his drink strong - tea with the bag left in.
There's little sign of his usual anti-gun stance.
There are some aspects of the Doctor that you might not like in this.

The other Doctor is a fugitive from an ancient war, of which the cyborg Gunslinger was also part.
Which of the two is the real villain of the piece? Are either?
Is the Gunslinger threatening the town, or protecting it?

The town boundary - crossing it summons the cyborg out of the desert.
The town undertaker (Garrick Hagon) will remind you off the one in Carry On Cowboy - he's quick off the draw with his tape measure.

There's lots of action, but it is quite a dark, contemplative story - examining some deeply ethical issues. Murray Gold delivers a suitably Morricone-esque score.