A strong first impression can be enough to make a TV show a hit for years. That's not always a good thing though, and with very few new series having an end goal in sight, and even the ones that do often being postponed or rethought if they get popular enough, more often than not beloved shows will be dragged out for longer than their plots and characters deserve.
Consequently, there are some iconic TV shows that started with a bang, firing on all cylinders and instantly going down as fan favourites, but drove that potential into the ground as the years went by. Still revered for their glory years, fans and critics fondly bring up their past successes in the hopes that one day, if they're lucky, these once-great series might be able to get back the magical spark that made them so memorable and interesting in the first place.
Sadly though, at some point you've got to call time and accept that it's never going to happen. There's no taking away what these TV programmes managed to accomplish when they were at their creative peaks, but if we take them as a whole, there's no denying that they've been bad for longer than they were ever good.
For two whole seasons, Sherlock could do no wrong. Over those first six episodes, Mark Gatiss and Steven Moffat created one of the best detective shows ever, not only striking gold by casting Benedict Cumberbatch and Martin Freeman as Holmes and Watson, but also having the narrative chops to create some genuinely compelling crime mysteries.
After wrapping up the main narrative at the end of the sixth episode though, which saw the series-long villain Moriarty commit suicide and Sherlock faking his own death, the creators had trouble finding a way to justify even more adventures for TV's best dynamic duo.
Consequently, while the next two seasons (and the Christmas special) still have their moments, the quality of the plots and the overall writing couldn't hold a candle to those earlier episodes, leaving the two leads to do most of the heavy lifting.
Where it used to promise a tight and concise crime thriller every single week, by the time the fourth season came around the narratives themselves played second-fiddle because of just how bloated the episodes had become, with the characters themselves being the only reason to justify tuning in every week.