Thankfully, the Sci-Fi Channel chose not to hold the second half of this season for several months in some vain attempt to stretch out one of their few successful properties. The nature of this particular two-parter was a bit more subtle than usual, and it was good to have the previous episode relatively fresh in mind before tackling the conclusion.
The first half of the season left off with the apparent revelation of Weir's death and the discovery of a massive Replicator fleet. With humanity in the Pegasus Galaxy under immediate threat by the Asuran onslaught, it's the usual matter of strange bedfellows. The Wraith already working on the problem of the Replicators is the first unexpected source of help, and soon thereafter, Larrin and her people (from "Travelers") join the fray.
Most of the episode is devoted to the process of bringing this unlikely alliance together, once it is clear that the Asgard upgrades to the SGC arsenal will only help in battles of limited scope. Considering the fact that the alliances were a foregone conclusion, the writers did a great job of keeping the interaction with the Wraith and the Travelers interesting and fresh. In particular, the captured Wraith working with Team Atlantis is still a great addition to the recurring cast, and hopefully he will appear in the future.
The interaction between McKay and Carter was particularly interesting in this episode, because it provides insight into Carter's place in the Atlantis dynamic. McKay eventually figures out a solution to the Replicator problem, but it's not a quick process. Most of the time, McKay works out a technical solution in a matter of minutes or hours, and after some last-minute adjustments, the problem is solved. McKay gets to have the inspiration but also the benefit of a collaborative process getting there.
The writers resisted the urge of allowing Carter to step back into the technical genius role, which had to be very tempting. Instead, she made a key suggestion, but otherwise left the execution in McKay's capable, neurotic hands. That's not to say that Carter's command presence is entirely convincing in the episode; her attempt at correcting Ellis and his attitude was played too softly. That's an odd way to describe it, but that's exactly the word that comes to mind when watching the scene. However, it's now quite obvious that Carter is not intended as the "savior" of Team Atlantis; if anything, her presence has been downplayed significantly.
I'm also not particularly sold on the idea that the Asurans have been annihilated. Leaving the final minute of the episode aside, the circumstances were far too "clean" given the threat level involved. While one could argue that the Replicators served their purpose by muddying the waters with the Wraith even more, they had plenty of potential as an ongoing enemy.
That said, the ending could be interpreted two different ways. One could assume that more than one copy of the Weir Replicator survived, along with enough of the Asurans to allow the writers to revisit them in the future. Or, going in a more intriguing direction, it could have been the true Weir, alive after all, leading a secret agenda against the enemies of Team Atlantis. Either way, it's great to know that Torri Higginson won't disappear completely.