As I've discussed the latest series with more and more people, I've noticed a distinct dichotomy in fan reactions to the new Doctor. Capaldi's Twelve appears to be a "love him or hate him" kind of character, with very few having a lukewarm reaction. It made me wonder why some can't stand him, while others think he's the best thing since sliced bread.
Then I got to wondering why any Doctor appeals to certain fans and not others.
Perhaps the most noticeable schism in fandom lately has been between fans of the Classic era who don't really care for the more recent stuff and fans of "NuWho" who just can't get into the Classic stuff. For ease of discussion, I'll call the former "strict paleowhovians" here, and the latter "strict neowhovians" (to differentiate from my usual use of paleo/neowhovian as mere indicators of which era of the show a fan first saw).
I know, for example, a significant number of strict neowhovians (SNs) who are none too impressed with Twelve. Conversely, I've come across a fair number of strict paleowhovians (SPs) who just really don't like Ten. The reasons seem to be similar, with opposing sense: the SNs don't like Capaldi's depiction because he's "too mean," while the SPs don't like Tennant's because he's "too emo."
But what about the rest of fandom—those who fall under neither SN nor SP umbrella? Those of us who like at least some of the stories across all fifty-plus years of the show's history still have strong opinions about each Doctor, and no fan's likes and dislikes align perfectly with any other's. Some can't stand Hartnell, and others think him an underrated gem. Some feel Tom Baker will always be the archetype against which all other incarnations are measured and others find him irritatingly self-congratulatory.
So what are the key qualities about any given Doctor that set him apart from the rest, and make him climb someone's best of/worst of leaderboards? Or is it qualities of the fan that dictate a Doctor's reception? (There's undoubtedly a master's thesis in there somewhere...) I suspect it's a combination of both, but here are my completely unscientific speculations about what some of each of those might be.