So I'm a johny-come-lately to this one... didn't really discover it until it hit Netflix about a year ago, got through a couple seasons of it and a season of Torchwood, and even though i loved it i got dragged away and it took me forever to follow up.
It didn't impress me at first... and a two-parter involving farting aliens about four episodes in almost killed it for me entirely. But I decided to give it a little more... and suddenly, it delivered. The episode "Dalek" was a great story that gave me a little background on the Doctor, being new to this and all, and had Christopher Eccleston going back-and-forth between manic and deadly serious. I'm not sure at what point it happened, but at somewhere between the first and second season I decided that this was the BEST SCI-FI PROGRAM OF ALL TIME. No exaggeration... sorry Star Trek TNG, Firefly, Farscape....