I deliberately waited for the annual price reduction to get Series 6 for £17.99, but I really don't know what people are complaining about calling Series 6 the worst season ever - do they not remember Series 3 with its barely daytime-soap-opera-quality B plots? Only the main storyline was any good and the rest was padding until the very end.
Series 6 does repeat one major event from earlier in 24's history but with greater consequences, develops another character from previous seasons to a much greater degree and continues the theme of Jack and family just like the first two seasons. The overall political sabre-rattling between the superpowers is also well written and acted. There's one event that's repeated for the third time and that grates a little but I enjoyed the rest.
Other than Series 1, Overall I have enjoyed the 4th series as second best, this latest season is on a par with series 2 or 5 but simply ends one plot and begins another rather than padding out the one story. Ironically, the writers' strike might be the best thing to happen to the show, it'll give more time to make series 7 something new. The ending is much calmer than in previous years because the biggest fireworks happened earlier, but there's nothing wrong with some emotion rather than just slam bang action throughout the entire 18 hours.