The first half of this important two-episode arc set the stage for resolution of several plot threads, most notably the fate of the Athosians and Teyla's child. It also marked the return of Dr. Carson Beckett, an event completely ruined by the SFC promotional department. Even so, there was considerable excitement regarding his return and how it would be handled.
Sometimes bringing back a beloved character, especially one that has been dead for an entire season, can be problematic. Such events tend to overshadow everything else and disrupt the flow of a season arc. Beckett's return was logically handled within the context of Michael's grand scheme; the connections to previous continuity made sense of the situation. Even so, the writers felt the need to add endless comments about how great it was to have Beckett back, and they became distracting and unnecessary by the time the episode was over.
The attention on Beckett forced a simpler structure: save Teyla before Beckett's biological breakdown clock expired. That gave the episode a certain sense of balance, with Teyla's plight getting plenty of attention. Frankly, I found that to be more interesting, because that was the plot thread that would have to continue into the near future. Beckett was obviously not coming back for the long-term.
While Michael's plan for Teyla's child was somewhat predictable, I was expecting the usual late-minute rescue. This is where Beckett's unique situation tossed a wrench into the normal mechanics, and his return became a lot more meaningful for me. If any other team member had gone for Teyla, Michael's would have been toast. Instead, the Beckett clone's inherent nature gave Michael the upper hand, and Teyla and her child are still in Michael's possession. That certainly leaves Team Atlantis in a bad way for the season finale.
This episode also serves to pass the medical torch to Dr. Keller more completely and logically than the previous 18 episodes ever managed. Keller and Beckett worked well together (if only to make the requisite exposition a lot less painful), and the writers took the opportunity to show how similarly they can approach novel problems. But a delayed transition shouldn't have been necessary, and after this much time, there will definitely be Beckett fans pointing out how inferior Keller is in comparison.
Generally speaking, however, Beckett's return is just a bit too invasive to the story, especially at the end. The final act is interminable, with dialogue clearly designed for nostalgia and fan service. Some of that is warranted in this case, considering that Beckett was brought back due to high demand, but there's such a thing as going overboard. When character like Carter, who never really knew anything about Beckett, take an unbelievable amount of time saying goodbye, it's an exercise in excess.