Excellent, and far and away the best episode of the series and one of the best episodes of television ever. I was bawling for half the damn episode. If this doesn't earn Emmy nods and other awards for John Noble's performance or for writing then that's a crime.
They just delivered on every level, from the brilliant teaser with the window on alt-Manhattan (with airships!), the 80's Fringe intro, the excellent de-aging of Walter and Nina, the dramatic portrayal of Walter's desire to save his son at all costs (and indeed the costs were huge), and showing the Observer saving him and his son.
And they did all of that without the benefit of most of the rest of the great ensemble cast. Brilliant episode, and let's hope we see more of the same in the future instead of more focus on the freak of the week type episodes.