And now the 60's become the 70's, black and white becomes color, and the funny little dark-haired Doctor becomes tall and rather dashing, with rapidly greying blond hair. This is the point, as far as I've seen, when the Doctor really comes into his own as a leading man and an action hero. Jon Pertwee is actually a tiny bit older than his predecessor, but you'd never know it from the Doctors they play. The Third Doctor actually physically grapples with his opponent, usually employing the kind of karate chops that define cheesy 1970's entertainment (which this most certainly is). He also has a spectacularly horrible fashion sense, and he excels at balancing arrogance and compassion.
Many fans lament the fact that this Doctor spent his first three seasons confined to Earth, but I don't see that as so much of a disadvantage. First of all, there's the classic Who problem of going to a far-off planet only to find that it looks exactly like the English countryside or the inside of an office building. The trapped-on-Earth years avoid this nicely by actually keeping the Doctor in office buildings and the English countryside, and letting the aliens come to him.
More importantly, staying on Earth allows for a stable supporting cast. Brigadier Lethbridge-Stewart brings something special to the series all on his own. Honestly, I've never figured out if he's a bit of a parody of a certain British stock character, or if he just embodies the type perfectly. Serving under the Brigadier are Sargeant Benton and Captain Mike Yates. Yates has a few great character moments along the way, but if Benton has a moment to shine, I've yet to see it.
Then, of course, there are the companions. I've really, really tried to like Liz Shaw. I felt like any female character who was written out of the show for being too intelligent and educated must be worthwhile. Unfortunately I just find her boring. On the other hand, I've had exactly the opposite experience with Jo Grant. I was wary of her as the supposed ditz who replaced the smarter Liz, but the more of her episodes I've watched, the more she's become one of my very favorite companions of all. She is certainly scattered at times, but she's also a fleshed-out character whose relationship with the Doctor follows a real (if subtextual) emotion arc. I would also argue that she's the first companion who the Doctor falls in love with, at least a little bit (but that's a whole entry for another day). And after Jo's departure, of course, comes Sarah Jane Smith, who's a great character when she's written well (and I've yet to see an episode where she's written better than in her first appearance, "The Time Warrior").