Meme-y mood

I feel like talking about something but not like thinking of what to talk about, so you tell me. I am making up my own meme here.

Name an episode (or episodes, as many as you like) from one of the following shows and I will tell you the following about it.

Doctor Who is of course preferable (modern or classic), but also Star Trek: The Next Generation and Firefly are fair game.

What I like about it.

What I don't like about it.

Favorite line.

Best performance.

A scene/idea from it that's particularly interesting to me.

Something I would have changed to make the episode better.

An idea for a fanfic relating to it.