I finished Fringe! What an ending! The whole final season wasn't something I would expect from a TV show, but I'm glad Abrams was able (and allowed) to pull it off. Spoilers follow.
I think seasons 4 and 5 are how DC Comics fans feel after a few decades of reading. New timelines, not trying to go back to the old one, piecing together what is and is no longer canon...
I suppose I could give some snarky comment towards FOX for capping it at five seasons, but there is something to be said about closure too. However, another season with a smaller story-arc and one-off Fringe cases would also have worked well if they kept the character growth (Astrid needs more!) and made it interesting.