Compared to the typical episode, I found this story to have more of a 'comic book' sort of feel to it.
The gang, complete with their attire, hideout and transport, almost have a sort of 'Mad Max' feel to them, but I actually quite liked that, making them a different and more colourful group of villains than the norm.
The episode is very well written and paced; the only scene that does drag for me is when McCall goes to visit his old contact from his days in 'The Agency'. Although I get what they were aiming for, it is, for me, the only scene which slows down an otherwise great episode.
Doctor Elly is a good character, not being afraid to stand up to herself nor the gang. I would have liked to have seen her return in a later episode.
[Minor spoiler] McCall's climatic calling out of the citizens to stand up to the gang might not have been completely believable in a more standard-based episode, but here in this more comic book fare, it just about works. [End of mild spoiler]
All-in-all, this probably stands as one of my favourites of the series. I like the setting and its comic book feel, and everything about it.