I have one huge gripe with the finale - Mike undermined his players' agency by having an NPC finish off Strahd! Yes, they had to remember a poem to summon her, so it's not a terrible move, but it still left his players watching someone else win the fight!
The anachronisms around D&D don't bother me. For something like that, getting a resonant reference to D&D as people play it today was probably a lot more important than getting the details right. The Demogorgon miniature from season 1 was not available IRL at that time, so it's something the show has always played with.
Overall, a good send off to the series. Easily the best part for me was the second half of the episode, where we got to say goodbye to everyone and see them get their happily ever after.