For starters, I'd say it's always welcome when the writers remember a piece of mythology that seemed forgotten - the return of the bald mystery kid from season 1, now confirmed to be an Observer, was unexpected and intriguing. And seeing the glyphs in context was a nice touch. The action was also well done, with Peter teleporting, Olivia figuring out that her gun doesn't work in the pocket universe and reacting in mere seconds ... I already said that, but that ability the Observers have to pop up from nowhere is REALLY spooky ! Speaking of spooky, I don't like Windmark's little smile when witnessing Peter's new abilities. I don't like that one bit : can the Observers now "hijack" Peter ? Anyway, you can see Joshua Jackson incorporating some Observer "traits" in his acting in the last scene ( something in his eyes, in the way his head moves ... ). There were some nice emotional scenes ( Etta's last message, Peter and Walter's talk ) , even if not as much as last time.
Which doesn't mean I have no complaints. First, except for a walk on the ceiling, this episode was not as eccentric as the Alice-inspired title would have led to believe. Come on, laws of physics don't apply in this "pocket universe", and you don't really show it ? Second, I would have liked at least one small clue regarding the plan, or Donald's identity ( I bet he's a devolved September ).
All in all, a transitional episode.