There's the general idea that 99% of television is crap, and while I won't say that's false (regardless of exact numbers) it is no excuse to call the remaining 1% the same. Television as a thing is something I don't like, and can't stand it most of the time, with commercials and stupid reality shows, irrelevant news and empty sitcoms with canned laughter.
But there are television shows, series and documentaries that I'd call works of art.
Arrested Development is probably my favorite, Carl Sagan's Cosmos is another, and as far as American television goes, X-Files, Lost, Dexter, Mythbusters, Seinfeld, Curb Your Enthusiasm and Six Feet Under. But I'm a big fan of British television too: Spaced (from the guys of Shaun of the Dead) is a masterpiece of comedy, The Office, Extras, Black Books, Monthy Python's Flying Circus, The IT Crowd, Flight of the Conchords (not British, but similar style) and Garth Marenghi's Darkplace Hospital; and some dark crime/mystery/drama/science fiction stuff like Life on Mars, Ashes to Ashes and Messiah.