Cracked has an infographic (selection above) illustrating how long-running TV shows rise, plateau, decline, and die a slow death over time. Scott Edelman at blastr thinks that it's particularly applicable to science fiction. I agree, and Stargate SG-1 springs immediately to mind. That show lingered on too long. But episode 200, which was explicitly fan service, made it all worthwhile.
Which science fiction shows do you think suffered particularly prolonged deaths?
Link via blastr