Every season takes a somewhat different tone. The general consensus is:
Season 1: The best
Season 2: First half too many cliches, second half pretty good
Season 3: Fine but unmemorable
Season 4: Strong finish
Season 5: Wait, why is there a season 5?
I concur...2nd season especially had sci-fi cliches including time travel, parallel, universes, etc.
Season , to me, felt like they were REALLY trying to get back to the season1 feel.
I think that's one of the reasons why season 5 felt so horrible..