In a season marked by more character exploration, the second half of that effort has been hit or miss. Fans were divided over the previous two episodes, and this installment, focusing on John Sheppard, will probably fall into the same category. It's an unusual episode, to say the least, because most of it takes place on Earth. It's a break in format that gives the story an unusual scope.
The plot is tied indirectly to "Miller's Crossing", where it was revealed that researchers on Earth had been working with Replicator-derived nanites for potential medical breakthroughs. It seems rather obvious that research would be conducted on creation of pseudo-Replicators with defined operational tasks. And given the luck humanity has had with the Replicators up to this point in the franchise, it was inevitable that the project would go horribly wrong.
That's a fairly thin plot, however, especially when the Replicator in question is programmed for military purposes and acts like Robert Patrick from "Terminator 2". It amounts to Sheppard and Ronon teaming up with a McKay stand-in from "SG-1" and hunting down the bad guy. Two unusual twist give the episode more to work with, and the result is a much better episode than expected.
First, there's the reason why Sheppard is on Earth, and the reason why he becomes the best man for the job. His father has died, and he returns home for the funeral. His remaining family and ex-wife are somewhat remote with him, and it turns out he's been the black sheep of the family in more ways than one. Not only did he choose a different path than his father would have liked, but it clearly led him down avenues of secrecy that damaged his marriage.
That connection becomes important in the uncovering of the Replicator project, including the true nature of Ava Dixon (played by the gorgeous Emma Lahana). Ava turns out to be a Replicator herself, but one programmed to focus on emotion and empathy. This makes things a bit more complicated, especially at the very end. Her "survival", such as it is, has all the hallmarks of a plot bunny, just waiting for some future episode to pick up the ball and run with it.
While using the ex-wife as a source of classified information felt contrived, given Sheppard's special brand of access, it fit within the context of the episode and kept much of the focus on Sheppard and his personal issues. Given the circumstances, his measured treatment of Ava was revealing. Not all character development requires a big, dramatic moment, and this episode did a capable job of proving that principle.