(Note: This review covers the first half of the season finale event. A subsequent review will cover the second half.)
Two things seem to have been in mind when constructing the final arc of this season. First, that Tony's character motivations needed to be addressed more directly, and in a way that touched directly on the overall theme of the season arc. And second, with an eighth season already a given, these events had to flow logically into the next leg of Jack's redemptive journey.
Even at this point, it's fairly clear that Jack will not be cured by the end of the season and that CTU will not be restored in the final episode. Jack will be lucky if he's even conscious by the end of the season. Tony and his terrorist friends really put him through the ringer, complete with spinal taps, and he's not in a position to save himself. It's just one of the more shocking portions of the episode.
The other is the writers' decision not to turn Kim into a defenseless victim, as they did all too often in previous seasons. Instead, Kim actually gets to use some of the skills she learned in her brief stint at CTU and show a bit of spunk in the process. Kim has always been treated poorly by the writers, who never seemed to figure out how to make her more than the hot little victim, so seeing them play on the expectation of further such failure was a nice touch.
Ever since he killed Agent Moss, it has appeared that Tony was unquestionably one of the terrorists, and his desire to move up in the ranks appears to be a nice bit of symmetry with his activities in Emerson's crew earlier in the season. But something about the timing, as well as his strange insistence, makes it quite possible that his motives are just as murky as they were at the beginning of the season.
All of which adds up to a lot of great material for the episode, which is good, considering that the subplot involving Olivia and Ethan is a bit too simple. For one thing, Olivia has the worst poker face in the history of "24", and it's hard to believe that she didn't recognize the collusion between Aaron and Ethan, when they were practically conspiring right in front of her. Why in the world would she let Ethan out of her sight before checking the data card, anyway?