With an episode title that references the Bishops, I was hoping that the long-running plot thread involving Peter and his origins would finally come to a head. Instead, there was a completely different connection to the Bishops. While it wasn't quite what I was expecting, it was still a solid episode compared to other recent offerings.
As it turns out, Walter Bishop is not the only member of the family to have a hankering for weird science. That seems to be a trait that was handed down from his father. The connections to the Nazi Reich and its own obsession with "fringe science" grounds the series in an unexpected way. In a sense, the entire series is now the story of what might have happened if the gruesome and bizarre experiments and theories of Mengele and his contemporaries had led to a new generation of equally amoral scientists.
In historical terms, one might say that is exactly what happened in the real world. Yet in this instance, it all came down to Walter Bishop and William Bell, experiments they conducted, and the fallout in this generation. Considering the fact that I'm a sucker for stories like this, where it's just as much about the past as it is the present ("Lost", "X-Files", "Harry Potter", etc.), I appreciate how the writers are giving the current crisis such a compelling origin.
I will admit, however, that there is a certain cliché to pointing back to the Nazis. Taking "Fringe" along with the other three examples I gave of stories of similar depth, three of them trace back to the Nazis or some analogue. It remains the go-to specter of the past to reference when something monstrous emerges out of history. I personally don't have a problem with it, since it works for a reason, but I think some will roll their eyes and wonder if writers will ever think of something different. (Speaking for myself, I hope not, since that would mean something even worse than the Nazis will have replaced them in the collective unconscious.)
In terms of the technology at the center of the plot, this kind of targeted biological weapon has been a matter of speculation for decades. There are many who believe that such technology already exists. It probably wouldn't be something that could be developed in someone's basement, but it's much closer to actual science than most of the "fringe science" that has been explored.
There was a nice bit of tension between Peter and Walter, even if it lasted only so long, and Walter showed some of the dark side that hasn't been quite so obvious this season. It's sometimes hard to remember just how amoral Walter has always been, and that he is likely to be cast as the original villain of the "Fringe" story, given his abduction of a young boy from a completely different universe. It's not at all surprising that he would kill someone in the name of his family.
Of course, it wouldn't be "Fringe" if there wasn't some odd convenience in the "science". I may be recalling this plot point incorrectly, but I believe Walter explains, early in the episode, that the toxin changed the ability of the blood to oxygenate, thus killing the victim. Walter himself is later exposed to the toxin himself, but all he needs to recover is a bit of oxygen. That shouldn't have worked. If he was already affected enough to start gasping for air in the basement, then his system was already saturated enough to continue killing him regardless of whether he was moved! Similarly, that inhaler for asthma wouldn't have made a bit of difference.
Even so, the context of this particular episode allowed it to transcend its stand-alone aspects. This was more than just connecting the episode to the rest of the season through a couple lines of dialogue; this was placing the entire series in historical perspective. It may not have worked for some, but it worked for me.