Over the last few months I've been working my way through the whole original 79 episodes, in the remastered versions, which are beautiful and a massive improvement on the originals: properly saturated sixties colour and basic CGI to replace all the dangly models, which does the job and is not intrusively offputting (whereas the models were).
One thing I noticed is that, whilst there are many excellent and thoughtful episodes, several written by some quality SF writers like Harlan Ellison and Robert Bloch, towards the end, especially in the third series, there were rather too many really stupid - "this planet is exactly like the USA if 'X' had happened, but light years away."
The stupidest one of all is one where they find a 'barbarian' tribe of white people oppressed by a more civilized group of "Asiatics'. It turns out, in an amzing example of parrallel evolution, that the vicious barbarians really have a secret religion worshipping the US constitution - which used to be theirs too - and with help from Kirk and co., will finally be able to understand and recover what is implied is their rightful place as the dominant culture. Ludicrous and not even the lightly amusing way that some of the more silly episodes are.