Last week I asked "What is the next serious fantasy or science fiction sub genre for television?" Why don't we take a look at the groundbreakers so far:
Horror (The Walking Dead; American Horror Story)
Paranormal Romance (True Blood; Buffy the Vampire Slayer)
Space Opera (Battlestar Galactica)
Epic Fantasy (Game of Thrones)
That leaves some strong contenders, like-
Contemporary Fantasy: It's our ordinary world, but there's magic.
Cyberpunk: The world sucks, and cyberstuff is everywhere.
First Contact: We meet the alien Other.
Slipstream/Magic Realism (Bryan Fuller has done some great work here)
Steampunk: Queen Victoria is on the throne, and computers have cogs and gears.
Time Travel: So many, many, many so-so series...
Urban Fantasy: Contemporary fantasy with a hard, noir edge, like The Dresden Files (which they did make into a series...a bad, bad series.)
Now, to be clear, there have been TV series that have explored all of these possibilities, but none of them have been as groundbreaking as shows like BSG and GoT. (And when I say "groundbreaking," I mean gaining widespread cultural acceptance outside of the F/SF community, from people who would otherwise ignore or dismiss speculative fiction.) Instead, there have been shows ranging in quality from Time Tunnel and Charmed to Firefly and Babylon 5 - but none of them "breakouts."