One of my favourites. Watched since Jon Pertwee was the Doctor (they were repeats, I'm not old enough to have seen his episodes the first time around). It's a different beast nowadays - hell, all of TV is. The writers have done really well though, for the most part. Didn't think much of Eccleston, but Tennant was fantastic, one of the best. Billie Piper was amazing as the Doctor's companion; her successors haven't come close, unfortunately. Only wish I could un-watch the Slitheen and Absorbaloff episodes.
In fact, it's close to my family's heart for another reason: my father's connection to Delia Derbyshire, who created the theme music; they were both part of the British electronic music movement of the 1960s and '70s.