I have recently been doing the same thing!
Me and a few friends have started from the beginning, watching all the stories that a) are complete, and b) don't have a reputation for being the biggest pile of bull ever produced.
Many may point out that this rule is cutting out some good stuff, but it's a long walk to their house from work, and after a tiring day at work, I don't have the energy to listen to the sound recordings of the episodes or anything like that. The second rule was going to be applied quite laxly, but then we watched Edge of Destruction, and decided to be a bit more careful in that respect.
We have just watched Tomb of the Cybermen, our first Troughton story. Meaning, due to rule 1, our next story will be the last Troughton story. Such a shame so little of his stuff survives, there are glimpses of a really interesting character there, the same as Hartnel, yet at the same time so different.
I'm also trying to persuade my friends that we should watch the 60s Dalek movies at some point:)
Doing this has made me realise how old the franchise is. Nearly fifty years! While I already knew the dates involved, actually watching it has made clear the full implications of this. The world has changed so very much since the show started, and the show has changed with it. I'm not just talking about things the show has done to "be cool" (celebrity casting and the like), I also mean the way the writers in different eras of the show have been brought up within different cultural and political backgrounds, leading to this gradual meandering drift in what the show (and, I would guess, television in general) is all about.
This has only begun to be noticeable at the moment, as this Who Marathon is still in its early days, I need to do more watching before I can really make a judgement on whether any of what I have just said is true, it is at this point an idea that has occurred from what we have watched so far.