In particular, I very much enjoyed the one thing that those who dislike this story universally single out for criticism, Jackie Lane's acting as the newly arrived companion Dodo Chaplet (who walked into the TARDIS at the end of the previous story). I thought it was great to have an assertive young companion - the first really since Barbara's departure (apart from the brief appearance of Sara Kingdom) - and for my money she rose to the challenge. Hartnell is on top form, and even his fluffs seem much more in character with the Doctor than with the actor. Peter Purves as Stephen has some great lines and even a mild love interest.
The other feature of this story universally mocked by the critics, the Monoids, actually seemed not too bad to me, for 1966 anyway. Certainly far far better than the forest creatures at the end of The Chase. They reminded me a bit of the Ood from The Impossible Planet/The Satan Pit. Their transformation from silent servitors to sinister overlords is creepy but compelling. And they supply the great punchline to episode two, when the TARDIS crew discover that the statue the Ark's human crews were building has been complete, but with a Monoid head.
I even liked the look of it. The gradual revelation that the forest has (as we are warned in the title of the first episode) a steel sky is well done. The Roman-style costumes of the human Guardians deliberately make us think of the Monoids as slaves. The surface of the planet Refusis, and its invisble inhabitants, are well done. The scenes of planets and suns in space are, at least, not too embarrassing.
This is from an era of Doctor Who (Season Three) that has had a bad press, but I've found myself very much enjoying three of the other nine stories (Mission to the Unknown, The Dalek Master Plan, and The Savages) and would probably have enjoyed The Massacre more in a different format. I also saw the last (and only surviving) episode of the following story, The Celestial Toymaker, on the Lost In Time DVD set, and thought it was great. So I shall look out for Galaxy 4, The Myth Makers, the rest of The Celestial Toymaker and especially The Gunfighters and The War Machines both of which apparently survive in full.