[Mild 24 season three spoilers below]
24 has seriously fallen off in quality, according to the author of this MSN article. While I agree with her on some of the problematic plot points -- Tony back at work just hours after taking a bullet in the neck? Jack's ability to get anywhere in greater Los Angeles in mere minutes? can't Sherry Palmer just go away? -- I disagree that the show has come anywhere near "jumping the shark" [see below]. The show hasn't exhibited any problems this year that weren't also evident last season, so these complaints ring hollow to me. Do some of the subplots falter? No doubt about it. Do some plotlines vanish utterly (what came of last season's assassination attempt on David Palmer?)? Yes. And do I keep tuning in each week, with no plans to stop doing so next year? You bet.
BTW, the other day AICN reported that next season, 24 won't start until January, halfway through the 2004-2005 season. While it'll definitely be hard waiting that long, I think this actually might be a blessing-in-disguise. Such a late start means that most likely the show will play out with a new episode every week, as opposed to disappearing during non-sweeps months as is the current practice. With such concerns gone, the writers may no longer feel the "pinch" of having to structure their season with a big plot twist at the end of each sweeps period (this year it was Nina's return, followed a couple of months later by Nina's death). Being unfettered from the shackles of sweeps periods may just be what the doctor ordered as 24 heads into a fourth season.
(On the jumping of sharks: Now there's a meme that I wish would go away. You can't talk about any series, be it TV, books or movies these days, without encountering people insisting they can pinpoint the exact moment when it stopped being good. I think that all this talk about shark-jumping has, you know, jumped....)