Naturally the previous seasons ended on cliffhangers that will never be resolved. I really hate season end cliff hangers.
The “cliffhanger” I disliked the most was “Revolution”, a dystopia series in a post-industrial world, in which electricity could no longer be used, because of the suppressive presence of nanobots with a sort of artificial intelligence.
I guess they just wrote themselves into a corner and could not make any resolution that would be satisfactory from a plausible perspective.