This is supposed to be a locked post for the future, but just in case you haven't guessed: This post contains major spoilers for Serenity. So be warned.
Overall, it feels like a nice, big episode to me. I don't know the difference between an episode and a movie; I can't tell where that line is. But this didn't feel like an episode padded out - it fitted nicely.
The plot owes a lot to Objects In Space, what with the Operative coming after River rather than the men with the gloves from the TV series. I also wonder whether Whedon will get flak for having (effectively) two black bounty hunters coming after the crew. However, where Jubal Erly was broken and River had to kill him as a result, The Operative is sorta noble: he knowingly does terrible things in order that a greater good can be served. He reminded me of Moses, not entering the Promised Land. And the Operative learns.
Not much for Inara to do, in terms of plot, and even less for Kaylee. This is a great shame: I wanted to see a lot more of Kaylee. Instead, she kind of fulfils Xander's role, telling Mal what he's actually feeling.
The Book/Wash thing. Shocking. Gutted. More so because of the double. There have been hints that something's coming, and with Book, you think you've seen it. Then whap.
Excellent opening. Very clever. I liked the reply thing [ I assume I meant "replay"... ], and I loved the justification for having the Alliance being after River: not because they've lost a weapon, but because of what was probably accidentally revealed. Makes far more sense.
River's fight sequences were great, and I know I'm going to watch them again and again, but I did feel that near the end, with the crew making a stand, it was practically a Doom homage. A first-person-shooter scene, almost. And I'm not convinced that Joss earned the shot of River in silhouette with swords. It might have worked better if the opening doors had seemed something of a threat. Then there could have been a flash-back. I dunno.
Marvellous dialogue, as ever. Cunning stuff from Mal when rescuing Inara and when leaving Miranda (although nicked from/homage to Galaxy Quest).
The origin of the Reavers was good. I expected more, actually, but I'll settle for it.
Want to watch it all again, now. Lord, I've missed those characters.