* This story contains plenty of spoilers for old TV shows. Do not read if you have been living in a cave and are yet to watch Dexter, Nip/Tuck, The X-Files, Heroes or Prison Break.
Years on air: 2006-2013
When Dexter first started, it seemed like we'd finally found a replacement for Tony Soprano - another morally ambiguous character who viewers could side with. Michael C Hall, playing a serial killer with a conscience, managed to tread that very fine line expertly in the show's first few seasons, deriving plenty of 'will he get caught?' tension out of his killer cat-and-mouse games.
His relationship with his sister Debra, as well as flashbacks showing Dexter's troubled childhood, showed it had a beating, bleeding heart underneath it's blood-splattered thrills.
But Dexter quickly ran out of steam after season four's John Lithgow-as-serial-killer plot, which saw Dexter left holding the baby after his wife's murder. By season eight, the viewer revolt was in full effect, and as for that ending, well, even Hall hates it.
Years on air: 2003-2010
How good was Nip/Tuck's first season? The premise was wonderfully bonkers: creepy plastic surgeons open up a clinic in Miami and treat a revolving cast of oddballs with issues that often reflected the doctors' troubled personal lives. Add in the occasional appearance by Escobar Gallardo - a thrillingly evil gangster that Dr Sean McNamara and Dr Christian Troy were forced to dispose of - and Nip/Tuck quickly became essential viewing. But the plot lines got increasingly bizarre and soapy - especially around McNamara's son Matt (later revealed to be Troy's son), who joined Scientology, had a child with Troy's on-off lover Kimber, became a meth-head and wound up in prison. By the time the show's absurd final season rolled around, even the cast didn't know what was going on.
3. The X-Files
Years on air: 1993-2002
Even Mulder and Scully's biggest fans - and there are a lot of them - would have to admit they probably haven't seen every X-Files episode. There sure were a lot of them, with 202 episodes and two movies - a third is is being threatened - airing over the show's nine-year run. At its peak The X-Files was brilliant viewing, capturing tens of millions of viewers each week by mixing conspiracy theories with overlapping stories about alien autopsies, shady characters called Cancer Man, circus freaks and eye-popping episodes like Home. But The X-Files ran around three seasons too long: David Duchovny bailed at the end of season seven, while plot lines got increasingly wayward and repetitive. Even the show's writers seemed to know its time was up - one of the last episodes was called 'Jump the Shark'.
Years on air: 2006-2010
No show has gone from hero to zero faster than Heroes. Its first season was one heck of an addictive, intricately-plotted fun fest with a cast of nobodies that perfectly fitted the show's storylines about everyday humans given superpowers being hunted down by a shady organisation. Season two was massively anticipated, but thanks to the Writers' Strike, quality was badly affected. Heroes kept going for two more increasingly B-grade seasons which reverted to obvious ratings grabs like girl-on-girl kisses. Amazingly, it's been resurrected for a fifth season called Heroes: Reborn. Our hopes aren't high.
5. Prison Break
Years on air: 2005-2009
They were stuck in prison, then they broke out and went on the run. Then they got stuck in a different prison, and had to break out all over again. Despite a perfectly paced first season, a compelling - if slightly blank - lead in Wentworth Miller, and a deliciously evil villain in T-Bag (he cut off his own hand!), Prison Break became a one-trick pony that tried to wring too much out of a one-note plot that didn't deliver anywhere near enough twists and turns. Anyone else regretting getting those prison escape route tattoos now?