As a performer and player of D&D who is a huge fan of CR, what I see that makes the show notable beyond all things that make D&D notable is the energy put into each game by the players, and how that energy is generated by their being performers first, and there being an audience second.
This is an attendant energy that is second nature for performers, so seeing it replicated in their home games isn't a surprise. They are also trained to tap into it, master a TV face, let situations breathe, not step on each other's lines, see an opening for a setup, tie a conversation in a bow, etc. That's what makes it extra entertaining for many beyond the Xs and Os of the game (apologies for the sports analogy). They just happen to have so many synergistic elements so well under control with a crack production team, and that is mostly a testament to Mercer who is authentic in his passion for the game and supremely gifted in all the right ways to play it.