(Ed. Note: I am currently writing up this review while recovering from having my gallbladder removed on Wednesday, 19 May. So if it seems like it's not as coherent as usual, blame it on pain medication and my need to take frequent breaks as I write!)
After such a portentous first half in the previous episode, it's surprising to note how straightforward this episode really was. If anything, much of what happened in this season finale was fairly predictable. But what it all adds up to is something of a narrative sleight-of-hand.
From a plot perspective, this seemed to be all about Peter returning to Alt-Fringe and discovering that the grass is not, in fact, greener on the other side. He wasn't going to find a father that was going to stop his war with Fringe Prime just because Peter was back where he supposedly belonged. And sure enough, this episode revealed that Walternate had used William Bell's designs to create a device to destroy Fringe Prime, using Peter (and only Peter) as something of a "fuel cell".
Peter and his true father have very little time together, which is an odd plotting choice. Instead, much of the attention is on Olivia. The first third of the episode spends an amazing amount of time on Olivia, William Bell, and Walter. It was great to finally see William Bell in action, and to see William and Walter confront one another on their actions over the years.
Walter's criticisms of William are all well-earned, but it's odd that William didn't defend himself or his decisions. Yes, Massive Dynamic was a means of profiting off the technology appropriated from Alt-Fringe, but it has also been shown as an important means of developing technology in defense of Fringe Prime. In other words, the technology stolen from Alt-Fringe is used to fund the war against Alt-Fringe, especially since Walternate has been forcing William Bell to help develop technology to use against Fringe Prime.
On the other hand, Walter can't deny that he was responsible for starting the entire mess that has, in the meantime, been William's responsibility to manage. That doesn't absolve William of his role in the war, but it does make Walter's criticisms a bit one-sided. Considering how little Walter remembers of his own role in matters, why would he assume he was the victim? (Then again, Walter is pretty damn good at selective morality, despite his progress over the past couple years.)
One of the best scenes in the episode was the confrontation between Olivia and Ginger Olivia. Not the fight scene itself (although that was very well done), but the conversation about the differences between their two worlds. For just a moment, it was possible to consider what might have been, had the two realities been capable of working together in common cause. (Of course, that conversation was part of the misdirection.)
The final confrontation at the opera house started off well, but it was a bit disappointing in the end. As soon as it was clear that the two Olivias were dressed identically, and Olivia declared her love for Peter, it was obvious what was going to happen. Just as it was clear that William Bell was going to sacrifice himself to ensure that Walter, Peter, and Olivia made it back to Fringe Prime.
But the simplicity of the moment also has some interesting implications. It's now clear that both Olivias have the same abilities, which suggests that there was a cortexiphan program in Alt-Fringe, just as there was back in Fringe Prime. It's also clear that Olivia is going to have quite a difficult time getting back to where she belongs, since she doesn't have enough energy on her own, despite her ability.
The switch between the two Olivias brings a certain symmetry to the season. The season began with Charlie being replaced by a shape-shifter, and now Olivia has been replaced by Ginger Olivia. While the shape-shifter was devoted to his cause, it would be interesting to see Ginger Olivia be a bit more conflicted in her role. Perhaps this will bring Ella's role into focus. One way or another, it seems less likely that this situation will be quickly reversed than the Charlie subplot, so the writers have definitely set up one hell of a third season arc.