My, have the relationships between the characters evolved ! Olivia's first meeting with Peter : I know she's under stress, but she basically threatens him ! But I also remember thinking, the first time I saw this scene ( or one of the first times anyway ) that they were so antagonistic that they could end up together, in a Leia-Han kind of way; and look where we're now. Peter and Walter : even MORE antagonistic, to the point where Peter physically assaults Walter when he's taking a sample from Scott. "I love you dad" was very far ! I didn't remember Broyles was such a jerk back then. Maybe because he was written to be some kind of roadblock for Olivia, like Skinner was in earlier episodes of X-Files ? Nina warns Olivia "like she'd warn her own daughter". Now we know she wasn't threatening, as we were supposed to think, she really considered Olive as a mother figure would. The season 4 reboot didn't come from nowhere, did it ?
Other little surprise : Jacksonville is mentioned. Did the writers planed that far ahead Olivia's arc ? Did they just find the name cool and used it more than once ?
Was it ever explained who Steig worked for ? He's an ex-Massive Dynamic, so ZFT maybe ?
We still don't know who Mosley was. Not an Observer, he's got eyebrows ( real ones, or else it would have been mentioned ). Maybe he was working for the military guy from " Fracture", the one who thought the Observers were spies ? ( Good intuition, by the way ) It doesn't explain how he's acquired futuristic weaponry and tech, but that's my best guess now.
The "other Walter" was puzzling, but "Black blotter" kinda answered that : Walter's return to Saint-Claire reactivated his fear of the man he was, the man Carla Warren died to stop, which sent him there. Are you currently rewatching Fringe, or do you plan to ? And if you do, are you discovering new things in hindsight ?