Two things you should know about me:
1. I love cop shows.
2. I love film scores.
And there was a small but perfect storm of these in 1996, when the TV series High Incident first aired on ABC. Here are the original opening titles:
But then, after a few episodes—maybe even just one—the theme music changed to this:
I mean, it's not bad music per se. It just suffers in comparison, since the original was so energetic, and the replacement is so... emo, for lack of a better word. Maybe the producers wanted to set a more downbeat tone, but that's not how I remember the show.
And it was a good show. I still remember the last episode. Jesus, that was heartbreaking.
Anyway. Music. The same thing happened to Veronica Mars. Here's how that show opened for the first two seasons:
And then this happened in season three:
I mean, come on. Just... come on.
Once again, it's not a bad choice per se, but given how much personality and texture and just plain attitude the original Dandy Warhols song had, the "remix" doesn't hold a candle. And I believe deadening the opening titles like that contributed directly to the show's decline and eventual cancellation.
So here's my advice to any current or future showrunners: make sure you have a good theme song when you start, and don't change it unless you have a damned good reason. You can update the visuals as cast members change, or add revolving "tags" like The Simpsons (see below), but don't mess with the music. That is your foundation.
Those notes, those chords, those specific sounds are setting the mood for your show. More than that, they are signaling continuity. They tell the viewer that yes, this remains the awesome show you fell in love with ten or more seasons ago. Keep watching.
Worried that your theme song will sound hopelessly dated after a decade? Pick the right music and it won't be an issue. Herewith, a few exemplars.
Stargate SG-1 (ten seasons):
Law & Order (twenty seasons):
The Simpsons (twenty-five freakin' seasons and counting!):
Here endeth the lesson.