Heroes, Season 1. Opened with a bang, went out with a wimper. The show made a steady decline over the past few seasons. The writing just dropped off. The strong heroes/villans started blurring lines, and too many new heroes without enough development of the core characters.
24, Seasons 1, 7, and 8. The first season was rock solid, one of the best shows that year. At the end of the season when
I was left wanting more. High energy, great plot, but a bit liberal on the real-time side; I used to live near LA, and there's no way you could drive to some of the locations as quickly as he did! The last season had the same kind of explosive action. Jack went down a very dark path, one that there would be no recovery from, save a presidential pardon (no, not a spoiler). Of course they left it open for a
24 movie, which I'm highly anticipating.