For anyone who hasn't seen Season Four I don't want to spoil anything about this finale, so I'll keep the comments general and brief.
The final episode here was good, with some expected results and a surprise. What was different was that the terrorist story was over with 25 or so minutes left in the story. That is where, I assume, they bridge Jack Bauer's new status and will link it to whatever happens in Season Five.
Overall, this Season Four was outstanding; some of the best television I've ever watched for pure "involvement." That's where this show excels: it gets the viewer totally hooked. I've only seen two years of this program as I am writing this: both on DVD - Season Three and Season Four. I thought Season 3 was good enough for me to purchase this Season 4, and it did not disappoint me. In fact, I think I enjoyed this season more. It was fascinating all the way and the stories were better written than the previous, although I enjoyed the main villain better in the third season.
I would imagine none of the stories in any the seasons would be credible because, for one reason, just too many things happen in a 24-hour period here, but credibility-aside, it makes for great entertainment....which is usually why we watch any fictional story.
For anyone who hasn't seen this TV show, I highly recommend this fourth season. You won't be disappointed. See it on DVD. That's the only way to watch it. I mean, why have commercials interrupt the constant suspense?