Season 1 was worthwhile on its own; a fresh show with beautiful people using quirky dialogue in a compelling mystery.
Seasons 2-3 were worthwhile only insofar as building a complex mystery that would need a big payoff at the end.
Seasons 4-5 slowly revealed that there would be no payoff.
Season 6 admitted that the writers had no friggin clue what they were doing. Anybody mad about the Game Of Thrones finale needs to remember this BS.