If there's one thing I've been looking for over the course of the past couple of seasons, it's more depth for the Wraith. The first two seasons explored the origins of the Wraith and their unique physiology relatively well, but since then, advances have been sporadic at best. Most of the progression has come from Michael and the recently captured Wraith scientist.
This episode helps to change that, as the reproductive aspects of the Wraith are explored in grim detail. The writers manage to avoid too many exposition-heavy scenes, letting the brief glimpses of the process speak for themselves. This episode also explains how the Wraith managed to overwhelm the Ancients, despite the gaps in technology and evolution. All in all, it's a heaping plate of Wraith goodness.
The end result appears to resolve any possibility that the Wraith will quickly expand to take control of the Pegasus Galaxy in the wake of the Asuran defeat. The Wraith will continue to operate as competing factions, giving Team Atlantis the opportunity to counter them as effectively as they have to this point. This takes some of the pressure off the writers, in a sense, because they can't be accused of ignoring the latest shift in interstellar state of play.
This episode also addresses Teyla and her situation, which is a bit more mundane. She resents the thought of being handled with kid gloves by Sheppard, which is understandable, but this encounter with the Wraith forces her to acknowledge her role as the salvation for her people. Logically, she and her child won't be able to restore the Ethosian race alone, but they are vital until her people can (hopefully) be found. This realization is hardly surprising, but the writers made it work within the context of the Wraith conflict.
I found it interesting, from a character perspective, that Sheppard was upset with Teyla over lack of disclosure. I've felt, since the first stirrings of an impending Weir exit, that Teyla and Sheppard were being pushed towards each other. While this is an admittedly subjective interpretation, I can't help but wonder if part of Sheppard's annoyance comes from learning about Teyla's hidden relationship.
This has been a surprising season for "Stargate: Atlantis". After a quick start, the momentum seemed to diminish, but the last few episodes have been well above average for the series. Considering that the series has already been renewed for a fifth season, there's reason to believe that the rest of the fourth season will continue on the same path.