I watched it again recently.
Perhaps I've seen the premiere too many times because the flaws are becoming more glaring. It's still very good, and certainly iconic, but I do feel that the dialogue especially could have been handled better in places. I guess we can't know exactly what is down to the script being that the single-take nature means that a lot of dialogue is partially ad-libbed.
The plot also comes across as fairly contrived. There are much darker implications that would actually explain things, but it isn't clear if they were intentional. Otherwise it's only, 'the teachers are curious about a strange pupil and the plot needs a reason for them to end up in the police box'.
The other three episodes aren't bad, they just feel a little light in my opinion. For an educational story I would have preferred more information, or implied research into the era. Instead it's just grunting men in caves talking in simple English with monosyllabic nomenclature, talking about sun worship, fire and skins.
I will clarify though that I do think this is a good story, this is mostly relative 'but we love it so' criticism.