The problem with the final season was that it wasn't the final season. It was just another run-of-the-mill season in the show that meandered all over the place in order to fill the episode quota, then an incredibly weak and nonsensical "finale" tagged on at the end.
At least that's why I was disappointed, and I tend to try to stay optimistic for most of the shows I watch. Or at least hope the writer's have something more interesting planned than what they're currently showing, anyway.
In retrospect, I kind of wish the series had ended after the first season. It was pretty much a perfect story for me.