A strong and wonderful classic Doctor Who episode. Often cited as a high mark for both the First Doctor TV episodes and pure historicals in general, perhaps even used as a standard of quality for these types of stories going forward.

Sure, it might have the odd dodgy set or performance in the one-take marathon that is the First Doctor's era, and yes, the writing can be a little slow sometimes, but it largely holds up. I think the most effective aspect of this episode and where it gets a certain timeless quality to it (aside from the black and white minimizing the special effects weaknesses) is how respectful it feels towards the Aztecs. We are engaging with the era instead of treating it with stereotypes or dehumanization. Barbara gets to shine here but I really think it is a pretty well-balanced adventure overall. A pretty strong chapter in early Doctor Who.