Jack finishes as martyr. He has played this role many times through the series, sacrificing his humanity in the nightmarish choices he has made in service to his country and the unnamed thousands he has saved from various terrorist plots. So despite my issues with this episode, needing a death to ramp up "revenge rage" in viewers (when Jack had plenty of motivation with Cheng anyway), the ending where Jack takes Chloe's place is fitting.
The plot in the episode is simple, and it played out in the darker "Season One" scenario I laid out last week: Jack had to go after Cheng, so Kate leads a team to take out the sniper who has his rifle sight on Audrey. The writers play with the viewers, turning us one way and the the other--as if they were giving us both endings filmed for Season One--but they decided to kill her finally. And the next scenes play out to the textbook of berserker Jack (as seen in Season Eight) finding a new violent way to execute Cheng, Jack completely going against his advice to Kate earlier in the season about the emptiness of revenge (how it robbed him of the little bit of a life he had left). We now know Jack said those words hoping Kate could get out of the cycle of violence, yet knowing he could not.
There are three highlights of the episode: (1) the resignation, (2) President Heller's haunting last words about soon forgetting all this has happened, and (3) Jack admitting to Chloe she has been his best friend. Although part of me would have rather seen the Jack-Ryan ending, I realize this one is true to form--Jack as violent action hero and martyr--but it makes me wonder if there should be more episodes after this one. I'd watch Kiefer return, of course, but maybe they should stop here at 204.