I didn't like at all the premise of this season.
It was a different timeline, so many things were taken to a blank state (characters that died are alive again, some villains are back with their same plans...) and character relationship had to be rebuilt (Peter and Olivia, Peter and Walter...)
It seems pointless to watch versions of the characters you've seen growing for 3 seasons suddenly have their experiences and memories robbed for them. I enjoyed seeing Peter having to struggle with this, but I was hoping that everything would eventualy return to the original time line and back to how it was, but I think I was mistaken. It just feels WRONG to see Walter not remembering Peter. I mean, I enjoyed the chance in their dinamic, but as I said, I was expecting it to reverse back.
I give the season half a star more of what I intended to give it because I loved the last part of the season and some things, like the Observers' backstory, but I really disliked it as a whole.