Great episode (although I still like a couple other ones better). It was interesting seeing through River's eyes in the beginning. I wasn't fooled by River's plan, but that's probably because it reminded of a Heroes Unlimited session a long time ago where our DM pulled the same trick (if they're not inside the ship, look outside). But you have to give Joss and Tim credit for making such an interesting character based on something real and human, River's autism, instead of weird aliens stealing the show.
You just gotta love the little character bits they throw into each episode. Like when Jayne hears a commotion outside, pulls down a blanket revealing a stash of weapons, but he's just pulling it over him to go back to sleep. There was real emotion in the show, as they grappled with whether River is to stay or go, and her reaction. And a good, solid ending, defeating the bad guy in a very elegant way.
Firefly is on a streak of great episodes that easily matches Buffy or Angel at their best.