It's great. I knew nothing about the source material before watching the show and it is what pulled me in to watching Critical Role. Only issue I had was Scanlan's humor in the show is a little much. I have zero problems with the humor itself, raunchy humor is fine with me, it just felt like it wasn't well balanced and there's a couple dramatic scenes in the first couple episodes that get stepped on by a Scanlan joke. It's a lot more balanced in the source material because those episodes are 3-5+ hours long. Still the series finds its footing and does start to balance out pretty quickly. By the end I found it really great, though I admit I am a sucker for Found Family fantasy stories which is what this is through and through.

Also having seen the show originally without knowing what it was based on I still think the coolest aspect is that, since the source material are a DnD game, it means any time a character- hero or villain- survives or dies in a fight its only because that's what happened in the game. There's no plot armor or hand of the author as a result: if a character gets away from seeming certain death in the show you can go to the stream and see how the players managed to accomplish it within the rules of a game where any character can die. It's a fascinating way to tell a story and there are some really cinematic moments that happen in the original streams completely organically as a result.