My one issue with Orphan Black is that it often saves almost everything for the finale. That was more true than ever in this season, for better or for worse. Having all your plot threads reach a climax all at once can be incredibly satisfying, but you also run the risk of making the lead up seem painfully stretched and the payoff incredibly rushed (like Game of Thrones season 5). That isn't entirely the case with this season, but I do wish they could have spread the big moments throughout the season a little more. Now that I've seen how the story played out, I know that wouldn't have been possible. Still, it would have lent a greater sense of cohesion to the season. As it was, there were times when the show felt somewhat aimless this year, as if there was no central plot driving it, and the finale felt like it had a bit too much packed in. The episode just had so many plots running all at once that it became hard to follow.
As a result of this lack of narrative cohesion, this season emerges as one of the weaker seasons of the show for me (while still great). However, I do not at all think that this is the beginning of the "downfall" of the show. Far from it. The next season looks VERY promising, especially after all the twists of this episode. For the first time since the second season, I can clearly envision them having a single central narrative that carries through the entire season. There have been individual episodes that bring everything together (such as the fantastic 'The Scandal of Altruism'), but for the most part things have drifted apart as they went along. Next season looks to reverse that tide, which is perfect timing given that it will be the last season.
In case I have been talking too much about the season as a whole and not enough about this specific episode, I shall dedicate this section to the episode. I thought it was great. There was a whole lot going on, and there were some moments when the sheer amount of information became overwhelming. When I heard that this episode end on a cliffhanger, I was admittedly trepidacious. There are some unanswered questions from this season that I really wish had been answered in this season, but none of the cliffhangers introduced in this episode bothered me. In fact, I think they were kind if brilliant.
I hope my review has not come across as too critical. I've really enjoyed this show, this season, and this episode. It's mostly great, and I'm really looking forward to next season.