In my opinion the last season was ****ing horrible. When they told us that Walter had planted multiple videotapes and that they had to find each videotape in order to figure out how to save the world, I thought I was watching a show written by a kindergartner. The best thing about the early seasons was the interaction with the parallel universe, and that was all flushed down the toilet until the last couple of episodes.
The only good thing was that the last couple of episodes were 1000 times better than everything else in the final season. I almost quit watching halfway through the season, and the abomination that was the last season killed any interest I have in watching Fringe reruns on the Science channel.
Compared to Fringe's last season, the final season of Lost was a masterpiece. At least Lost kept you hooked right up until the very end before it left you bitterly disappointed.