One of the great things about Doctor Who is that with all of the back stories to watch through, and all the present stories to continue watching, there is a good chance that any given Doctor Who fan has watched the stories in their own, unique order. For example, I am perhaps the only Doctor Who fan to watch The Rings of Akhaten and The Gunfighters next to each other. I am also probably in a small minority who watched The Gunfighters after A Town Called Mercy, the revival Doctor Who episode that has The Doctor visiting the old west, as he did in "The Gunfighters". So many of my impressions were formed backwards.
The Rings of Akhatan was a gorgeous special effects spectacular, with many different alien races and computer generated space imagery that would have been amazing to anyone in the 1960s. And it was full of science fiction, and the Doctor behaving heroically. And for all of that, it fell (in my opinion) flat, or at least overreached its grip.
On the other hand, we have "The Gunfighters", which uses no science fiction elements (beyond The TARDIS delivering our crew to the Old West in the first place), and with a few wobbly sets. In this episode, The Doctor does very little that could be considered heroic, bumbling from one plot twist to another, managing to lose a tooth, and prudely refusing guns and alcohol thrust into his hands. His companions are similarly useless, and they manage to do nothing to help anyone. In addition, the plot is stitched together from history and romance, and is padded by many comings and goings to pad it out into four episodes. It is also a weird mixture of comic and tragic, with people dying (not always convincingly) mixed in with slapstick.
The one thing the two episodes have in common is singing. And a lot of it. "The Gunfighters" has a comic ballad sung to narrate the events, an innovation at the time and (as far as I know) one that has not been repeated.
"The Gunfighters" was also not a particularly popular episode, and is considered to be one of the episodes that drove a nail into the idea of solely historical episodes.
And yet, from my perspective, after watching the somewhat hypertrophied "Rings of Akhatan", the seemingly silly, charming "The Gunfighters" was a refreshing change. The Doctor, to me, is more convincing when he is in the middle of things that he doesn't quite understand, when he is muddling between double crossing teams he doesn't understand, then when he is heroically settings things right. And although some of the slapstick and black comedy might not be too everyone's taste, and perhaps this wasn't it at its finest instance, it still worked for me. With Doctor Who, there is little to nothing that I've heard all fans agree on, and this is why: that this quickly stitched together story from 1966 should appeal to me more than a well produced and richly done episode from 2013 is something that I can't really defend, or really even explain. It is just part of the endless charm of Doctor Who.