I feel as if I should start off with the original, 1960s series rather than recent adaptations of it, however.
Just a point of semantics, there is no such thing as a "recent adaptation". What's being produced today is the same series as what started in 1963. This also goes for the infamous 1996 TV movie, regardless what you might hear. The only "adaptations" are the two movies made in the 1960s starring Peter Cushing. Otherwise it's no different than, say, watching a Michael Moriarty episode of Law & Order from 1990 and then one of the later ones with Sam Waterston. Same series.
As noted, however, the series has evolved over the years. SFX have gotten better, the serial format has been mostly dropped, and the individual episodes are longer (though the original serials themselves told longer stories for the most part). The "classic series" was more about the characters than about the SFX. That's why people love it so much. The new series has kept much of that spirit - just the special effects toys are easier to use so there's a bit more "wham pow" in the visuals than there used to be.
I personally think there's nothing wrong with starting at both ends of the rope. That is, watch the newer ones and dip into the early history. In fact, from what I hear in doing so you'd be replicating the experience of the current stars: Matt Smith researched the role by watching 1960s classics like Tomb of the Cybermen (which he continues to rave about) and Karen Gillan made a point of watching the very first episode, An Unearthly Child, which she thought was brilliant, too. And as noted, the series doesn't demand you gave an intimate knowledge of what has come before, as it usually does a good job bringing people up to speed. The Eleventh Hour, the beginning of the current season, is as good a place to start initially as An Unearthly Child, the story that started it all nearly 47 years ago.
I would say that if you want an idea of how the series started, get hold of the DVD box set The Beginning, which has the first 3 stories from 1963-64 - An Unearthly Child, The Daleks, and The Edge of Destruction. All three set the scene very well. The first story, Unearthly Child, begins with a fantastic, Twilight Zone-worthy half hour introducing the characters, and then slows down a bit for the remaining 3 episodes, but they're still important in terms of seeing how the Doctor was originally conceived. The Daleks, of course, introduces the longrunning villains and if you're one of those "modern" viewers who wonders what the big deal is, try to imagine yourself a child or teen in the 1960s to whom this is all brand new. I get myself in that frame of mind and the introduction of the Daleks is still chilling. The Edge of Destruction was a "bottle show" but has some fantastic character work, establishes the TARDIS as a character in her own right, and was the first episode to get the show into trouble with parents groups (something to do with using scissors as offensive weapons).
I'd also recommend The Aztecs as an example of "historicals" - the non-SF storylines the show often told in the early days. The current series has tried to revive the spirit of the historicals, though with more overt SF storylines than the straightforward ones told here.
Dalek Invasion of Earth is notable for being the first "alien invasion of earth" storyline. Everything done since, particularly in the Russell T. Davies era, but also the Patrick Troughton and Tom Baker eras, too, owes something to this story, which set the template.
Once you've seen these you'll have a good feel for the early show. Of course many episodes are lost from this time, but BBC Video's done a great job putting them out on DVD. There's even a box set called Lost in Time that samples stories that no longer exist in complete form.
After you've sampled Hartnell, if the early era still interests you, moving on to Troughton makes sense. Sadly only a few of his stories still exist, but Tomb of the Cybermen, The Invasion (which introduced UNIT), and the epic 10-episode War Games (which introduced the Time Lords) are the real essentials, and they're all available on DVD.
Alex
