I started watching a week and a half ago and I'm at the beginning of season 3. I must say they keep it really interesting, it's not getting predictable. I miss the original music though. I loved that episode somewhere in season 2 (I think) when they play it at the end of the episode.

Did anyone ever noticed the Firefly spaceship in one of the first episodes of season 1? You can see it flying over the city from inside a building. I paused the picture and zoomed in. I would swear it was the Firefly.