I didn't really do a proper full review of this episode last time round, more of a quick reaction post. My general feelings are unchanged with a subsequent viewing but there are some things I could address in more detail and with a different perspective now.
I noted originally that this had some of the trappings of classic Who and it does because here we have the Doctor and companions arrive in the wrong place due to TARDIS navigation failure and get mixed up in something that has nothing at all to do with them. Nobody summoned him, no one is looking for him (despite the clever before credits teaser). It's a welcome change.
Also the frantic pace of Season 7 seems just a bit less frantic with this episode. Perhaps because the focus is narrowed to a very small number of characters and the others are just bit players. Even the Ponds are really just minor elements in this episode. Which is a welcome change given how Pond heavy the first half of the season is.
There are some fun echoes of past and future episodes in A Town Called Mercy (hey it's Doctor Who, we can do time travel). For example Amy calls out the Doctor on the way travelling alone affects him. The Time Lord Victorious anyone? And the Doctor finds himself Sheriff of a town and responsible for its citizens. Hmm, well that sounds a little familiar now doesn't it?
Whether those echoes are deliberate or fortuitous I don't know, but they do add an extra layer of depth to the episode on rewatching which is pleasant.
The core moral dilemma here is a good one I think. While the Doctor's pacifist tendencies have fluctuated wildly over the years depending on who's writing him (and even in the newer series he's pretty inconsistent) the notion of deliberately sending a man to die isn't going to sit comfortably with him. On the other hand it's made clear we're dealing with someone who did monstrous things for (in his view) the greater good. And that hits a bit close to home doesn't it?
hler-Jex seems to feel the need to justify his actions by probing and pushing at the Doctor. He knows what he's done, but doesn't really want to own the consequences. But as the story plays out he is forced to a position where he can't really ignore them any longer.
All of which makes it sound rather heavy, but it's not. It's mostly light hearted and fast paced. The humor is pretty broad, a bit too broad for my tastes at times, but it keeps things up beat. And of course all the western trappings are fun.
This isn't an episode that's going to go on anyone's best of lists, but it's solid and fun to watch. Which in reality is all I ever really ask of a show. Expecting Doctor Who to be bold, challenging and different on a weekly basis is in my view fundamentally misunderstanding what the show is.