I really liked this episode. Heart wrenching seeing Walter so maladjusted and unable to even look at Peter and sweet seeing him grudgingly admit to Peter's Faraday Cage idea being a good one.
This episode reminded me of the 'Angel' episode, 'Happy Anniversary'. Whereas that was freezing time, this is reversing time. Its to do with love, engineering and physics. Its to do with one person (Raymond, an electrical engineer) unable to imagine a future without the woman he loves (Kate, a professor of theoretical physics who has solved time travel). Of course this is paralleled with Peter who has had his love torn away from him as well.
As always a very well balanced episode. Concentrating on character dynamics as much as the case in hand. A real world situation with a science fiction twist, handled in a sensitive but not overly sentimental fashion.
I really hope that everything doesn't suddenly flash back to the way things were before. (As much as I loved the previous character dynamic, especially between Peter and Walter). I am assuming that at some point things will have to return to the other time line as Peter himself said that he was in the wrong place and needs to get back.
I think the writers of Fringe have been very clever this season. Essentially keeping the show's paradigm the same but giving it a little tweak to keep it fresh and interesting.
This is definintely the best show on our TV screens at present.