Not only can TV title sequences get you in the mood for a show, they can also be unbelievably depressing when they accompany a show that has Jumped the Shark™. Has there ever been a title sequence more soul-crushing to watch than the final season of Laverne and Shirley, when Shirley was gone, Lenny had abandoned Squiggy (to make This is Spinal Tap) and they had to bring in a bunch of kids just to do the "Schlemiel, Schlemazl" bit? Particularly sad is the shot that accompanies the now-inaccurate title -- Laverne dancing with two versions of herself, just to make it look like the show is still about more than one person.
Or how about the last seson of The A-Team? The new arrangement of the theme song -- which sounds like a very early version of a custom cell phone ring -- practically screams "we've been re-tooled in a desperate attempt to revive a show that should have been canceled two years ago."
And once the opening voice-over of Charlie's Angels contained the line "Two of them graduated from the police academy, the other graduated from a top school for models," you knew it was over, even if Aaron Spelling didn't.