Most TV shows that last more than three or four seasons begin the inexorable slide downhill. It's to be expected after so many episodes (especially those long US runs of 22+ shows per year). But there are some series that, for whatever reason, completely lose their shit.
Whether it's bending their own rules, implementing weird sci-fi tropes or resurrecting one too many characters, these are the TV shows that perhaps should have slowed down and concentrated on what made them great in the first place.
Reason: Too many characters, too confusing
Heroes was the show that everybody and their mum loved in its first season. It was fresh, exciting, funny, full of awesome characters and nothing like anything we'd seen before. But as soon as season two arrived, it had already lost whatever plot it had originally.
Far too many dull characters were introduced, far too many characters overstayed their welcome, and we simply forgot who we were meant to care about and why. Let's take Nathan Petrelli, for example. The airborne politician was shot by his brother from the future, but let's leave that aside, because when he was later killed by Sylar the power-sucking villain, Sylar got tricked by telepathic cop Matt into believing he was Nathan and he continued in that form for most of the next series. For a show to become such a jumbled mess was heartbreaking. This was the reason no-one cared when the always-going-to-be-disappointing Heroes Reborn arrived.
Reason: Network interference, sci-fi nonsense
The first couple of seasons of this Jerry O'Connell gem was pure sci-fi awesomeness. Quantum Leap for the 1990s. A small group go from world to world in the hopes of finding home.
Jump forward two more seasons and they're nearly all dead, they're fighting a weird alien race called the Kromaggs and O'Connell's Quinn Mallory (Quinn for short) has morphed into a totally new guy also named Quinn Mallory (Mallory for short, in case anyone got confused). Utterly bonkers and nothing like the brilliant show we loved at the start.
It's all Fox's (and later Syfy's) fault. The show's creator was pushed out, other suits came in and wrecked it, even airing episodes out of order for no reason. Maybe Sliders was the sacrificial show that had to put up with the crap so that sort of stupidity doesn't happen (as much) today.
3| Baywatch Nights
Reason: Hasselhoff taking on aliens
At first, this spinoff from Baywatch didn't sound like a crazy idea. Hasselhoff's character quits his job and starts a detective agency. Fair dos. But then…
Very quickly, The Hoff was battling everything from surfing aliens to serial-killer mermaids to unfrozen Vikings. He even got cloned at one point. Suffice to say, we don't think the whole sci-fi element will arrive in the upcoming Dwayne Johnson movie reboot. But we wish it did.
Reason: Made it up as they went along
While all die-hard Lost fans will insist that Damon Lindelof and Carlton Cuse always had an endgame, it's probably fair to say they hadn't a clue what they were doing from the moment they brought in the smoke monster, a never-ageing Jacob and the Dharma Initiative. It just went totally bonkers.
By the end, fans just accepted any explanations they received about the mythology of the show (what's a Frozen Donkey Wheel? Ah, don't worry about it. Oh, alright), and when most questions weren't properly answered at all in the show's confusing (yet brilliant) finale, it's hard not to get frustrated about the direction it eventually went.
Reason: Suddenly went inexplicably sci-fi and fantastical
If you've never seen this teen drama from the early 2000s and looked it up on Wikipedia, you'll be very confused to read about five paragraphs before suddenly the word 'Wiccan' appears. Eh? Where did that come from? It was a show about a university student living her life in New York. Coming-of-age stuff. Romances. Struggles.
Then, during the show's run, university student Felicity is sent back in time one year by her goth/witch roommate. Just because. Remember, this wasn't a show that was like Buffy from the outset. That wasn't in the brochure.
However, she uses this power to just get the man of her dreams rather than use her knowledge to avert major disasters or splash out in a betting shop. Not happy with her new life, she manages to track down a magician to cast a spell to send everything back to the way it was in the finale. What the hell was all that about? It's like if Seth Cohen suddenly became a werewolf in The OC.
6| Louis and Clark: The New Adventures of Superman
Reason: They got together and ran out of (sensible) ideas
The beauty of this underrated take on the Superman legend was the Moonlighting-style will-they-won't-they nature of the show (and Dean Cain being generally brilliant).
But as soon as they got together, interest quickly dropped, along with its general quality. They got married by their guardian angel (played by Bosley from Charlie's Angels), and actually time travelled with HG Wells. It went full Doctor Who and no-one got the memo.
7| True Blood
Reason: Everyone became a dick
The first few seasons of True Blood were the perfect antidote to Twilight. It was sexy, smart and funny, and made vampires cool again for another year or so.
But once it started venturing away from the original books it was based on, you found yourself wondering who you should be rooting for. Hardly any of them were likeable anymore. And Tara became a vampire. And Eric lost his memory and porked Sookie. And don't get us started on all the werewolves, faeries and ghosts. This show made Game of Thrones seem like an episode of Casualty.
Reason: Rapidly forgot the point of the show
Many of us transformed into Gleeks in 2010. We couldn't get enough of the innocent New Directions and their quest to be champions at singing (or whatever it was called, we've erased it from our minds). We even enjoyed its second season, and a bit of its third.
But fast forward to the sixth, and it resembled nothing like the show we were obsessed with just a couple of years before. Rachel had her own TV show (WTF?), Brittany's real dad was Stephen Hawking, and Sue became VP (really). It just went up its own arse and lost all sense of reality by the time it went out with a whimper.
9| Prison Break
Reason: They broke out of prison
The first season of Prison Break is up there as one of the all-time greatest seasons on TV, ever. But it was also one of those shows which had a concept that had nowhere to go as soon as they broke free.
Somehow, they managed to get four seasons out of it, until the point where it became a weird Ocean's Eleven/Fast & Furious hybrid in which Michael, Lincoln and co were working for the FBI while trying to uncover a government conspiracy involving their own mum. How the hell they're going to top it in the revival is anyone's guess. At least there's a prison, this time.
Reason: None of it happened!
After eight pretty excellent seasons of working-class hardship, the final season saw Roseanne win the lottery and kickstart a load of bizarre fantasy and 'as if' sequences involving everything from Jerry Springer, Hugh Hefner and Roseanne killing terrorists on a train. Yep.
If that wasn't bad enough, the final episode revealed that the entire season was made up in Roseanne's mind to get her through a really crappy life, including the death of her husband Dan. What the hell? It totally nullified the rest of the show to the point where you never wanted to watch it back. What's the point?
11| The Colbys
Reason: Took the Crystal Skull route
Dynasty was a load of silliness, but it was pure 1980s awesome silliness. Its spinoff The Colbys was more of the same, and revolved around another wealthy, upper-class family, who are relatives by marriage of the Carringtons in Dynasty.
The reason it only ran two seasons? It ended with an almighty cliffhanger that would have even made George Lucas reach for the remote. Emma Samms's character Fallon became stranded in the desert, and was seemingly abducted by aliens. Completely out of nowhere. And then the show was cancelled and we never found out what happened. But did we care?