After the end of the fifth hour of 24, I was worried that the show was going to get bogged down in a "prove the traitor" plotline; I should have given the show's creators more credit. By the time hour six was halfway over, the traitor was revealed--and by the time the episode wrapped up, the story had careened in a totally different direction. That unpredictability and manic energy made the fourth season of 24 a delight; this season continues the trend. I still have some bad feelings about the brother of the assassinated David Palmer; hope I'm wrong, but it's not like the writers to introduce a character and then abandon him so quickly.
Downside to this episode: very little Chloe and Edgar. These are the "everyman/everywoman" characters that every viewer feels like he knows personally (and many viewers probably feel like they have a lot in common with them as well). I don't know that any of us would like to spend a great deal of time with Chloe, but she certainly is entertaining to watch--the ultimate "fish out of water" character.
Still my fave currently-running series (thanks in part to the fact that Everwood is still on hiatus). If you're not watching, give it a try--you're not so far out of the loop that the episode-opening summaries can't catch you up on the core facts.