Since I've been kind of obsessed with Critical Role lately, here are some resources that I think are helpful for those who are either just getting into the show, thinking about getting into it, or are just curious about it.
The Critical Role Wikia is a great place to kind of get the rundown of what is happening in the show, from basic information about what happened in episodes to understanding the characters and the world they live in. Take precaution though, since it is filled with spoilers, but if you're someone who isn't too worried about that it's a wonderful resource to sort of get the basic understanding of what is going on. This is especially helpful because the first campaign has approximately over 100 episodes with a total of over 400 hours worth of content, so it's very handy.
CritRoleStats is a site dedicated entirely of keeping track of statistics of the show, from tallying up numbers of rolls to providing what pop culture references they make in each episode, among plenty of other things. It's a site run entirely by fans of the show, and the cast and crew use the site constantly themselves to check up on things.
Critical Role Source is a Tumblr that features much of the fanwork the community has to offer, including fanart and gifsets.
And lastly, Critical Role Funniest Moments has a compilation of selective clips from certain episodes which highlight some of the funniest moments of those episodes from the first campaign. Keep in mind that not all the episodes are featured, because I think there were some issues with copyrighted material which caused some of them to be deleted, so they didn't continue the rest of the campaign probably due to that delay. However, they have started make some for the second campaign. This was one of the first channels that I ended up watching to see what the show was about, and to get a general idea of how the show usually is with their comedy and how the cast interacts with each other, and I think it's a great starting point for anyone who wants to understand the show without getting too spoiled. Although I cannot guarantee that everything is completely spoiler-free, though, so again take precaution nonetheless.
Other channels similar to this include: CriticalGeminiHero, who has just started to make crack!videos for the second campaign. I really like her style of creating these videos, which she spends a lot of time and effort finding the right moments and doing a lot of effects to highlight the comedic parts. I highly recommend checking them out because they're genius and probably the best crack videos I've seen in a long time, especially for this fandom.
ETA: miya09 has kindly pointed me to the direction of a Critical Role primer, which is pretty much a quick overview of the entirety of the show and is a very helpful resource for those who are looking for a decent breakdown of not only what the show is about, but also for episodes and arcs throughout the first campaign without anyone feeling overwhelmed by the sheer quantity that they have to go through. It's very well put-together, and makes for newcomers to feel more at ease with getting into the show without feeling that intimidation.