Was that Chloes first time with a gun?
I do agree with you assessment of her, though. I hated her and hoped they would kill her off when the bomb went off at CTU a few seasons back. I do think she has come a long way, and I loved her character this season (and I thought it was brilliant the writers had her as head of CTU)
As far as the show, I think they left at the right time. I was really getting tired of 24, and to be perfectly honest I was really hating this past season. I did not think the UN part was bad, I just felt like 24 lost the "it" factor that made it so great.
With that said, once they announced the show was wrapping up I thought the really stepped it up a notch. Granted the writers were prepared for this to be the end (they even said they had been having "series finale" talks throughout the summer, so they were not exactly surprised).