It's really too bad the show had to wrap after four seasons. It was epic in its overall plot, but moved along too fast in season's three and four. The very best shows seem to be the ones that know their start AND end date, and the writers have the opportunity to create the full, envisioned, story within the timeframe given. In this case, it seems they were not certain of their future, so the show suffered in the end. In a better run parallel universe, this is on season 17.