Alright, you want something old? How about the longest running sci-fi series ever!? Something that's been running so long that the original episodes are in black and white, and yet still after 48 years and (to this date) seven hundred and seventy-seven episodes it's still full of fresh ideas and still retains the ability to strike awe in those who watch it.
I am, of course, talking about the one, the only, Doctor Who. I know it's seen as a nerd series elsewhere, but over here it's very mainstream, and ever since it started has been a quintessential cornerstone of British popular culture. Sure, there's some not so great bits in there, but come on, they can't all be winners, especially when you have so many episodes, but for every bad episode there's about a dozen great ones. The special effects in the old series can be pretty cheesy at times, but that's really part of the charm. Added to this is one of the greatest rogues gallery ever seen, including such classic villains as the Daleks, the Cybermen, and of course everyone's favourite renegade Time Lord and magnificent bastard par excellence, The Master.
Oh, and there's also that goofy time travelling alien guy, I guess. He's always good for some laughs. >.> Seriously though, the Doctor is one of the greatest characters of British fiction, a classic trickster archetype who prefers to outwit his opponents rather than overpower them, aided by neat gadgets including one of the most iconic time machines ever and his signature sonic screwdriver, and topped with a stroke of genius plot point that allows him to keep coming back no matter how long the show lasts.
Seriously, a show doesn't get to last that long and be brought back for another round due to immense public demand without doing at least something right.