Depends on the game. If I love it, like a Zelda, or Uncharted like you mentioned, I savor the moment and start doing everything you can do. That doesn't even limit itself to a first playthrough though, I'll happily spend 60 hours on KotOR again for the fifth time. Otherwise, if I start to lose interest in a game slowly, like when I feel a game starts to drag, or when I don't really like it but still want to see the ending, I speed things up and start ignoring anything on the side. If I'm not interested anymore at all for whatever reason, I just quit.