The Good
Overall, yeah, I'd say it's pretty fun. The animation is generally well done, the voice acting is great (it should be since the cast are professional voice actors by trade), and it has some pretty memorable sequences and story beats. In particular, I thought there were some great fight scenes, especially where the undead were involved. The undead look really good throughout The Legend of Vox Machina. If you have good, creepy undead you've already managed to go a long way toward selling me on your project. But I digress.
As someone who doesn't tune in every week to watch Critical Role, I really had no idea what this arc would be about. I know very little about the campaign that catapulted them into the livestream spotlight. Being unfamiliar with the arc allows for nice moments of surprise; for example, I was absolutely delighted by the villains of this season. The Briarwoods are so arrogant, imperious, and nefarious that I'm genuinely a little jealous that I didn't invent them first. Also, it's wild to me to see a big-budget cartoon featuring Vecna. Okay, they have to call him "the Whispered One" for legal reasons, but it's still damn cool.
The Surprising
It's interesting that the Crit Role folks decided to go full-on adult content with this series. I saw somebody complain about the swearing in the first episode; if they stuck around, I'm sure they got an eyeful of stuff they weren't anticipating. It's got plenty of bloody violence and some viscerally gross bits that I enjoyed. It's got depictions of torture and execution that are actually a little harrowing. It's got tits, cunnilingus, and anal beads. It really doesn't hold back in that regard. Caveat emptor.
The Critique
I know the character is beloved and everything, but the bard's musical interludes are the kind of thing that make me grind my teeth. The "theater kid" energy coming off those scenes is palpable. It's a relief when they end. This stuff is not for me, but I can definitely imagine that it will appeal to others. After all, people like Hamilton and go to see Welcome to Night Vale live of their own volition.
Also, although this is a common element of modern animated series, I still find the combination of traditional animation and CG graphics to be a bit distracting at points. It's not a deal breaker, but even with all the money behind it I can't help but think that the pairing can look a little cheap.
There are also some artifacts of translating a D&D game to the screen that become narrative problems in the series. For one, it feels like there are too many characters in the main cast. Crit Role plays at a big table, but as the protagonists of a story the large cast feels crowded. Some characters (the gunslinger, the twins, the druid) get more narrative weight, but that makes some of the other characters (the barbarian, the cleric) feel unimportant enough that it's not clear on a narrative level that they really even need to be there. At one point, the barbarian got knocked out and it wasn't until he got up later that I even remembered he was in the cartoon.
The concessions to the players made during a game also make the story an odd fit to a cartoon series. For example, one of the players in the campaign couldn't make all the sessions due to filming a tv show, so her character wasn't present for all the action. The show tries to shore that up by having her character experience a crisis of faith that entails her taking a solo trip to get her mojo back. That's a good enough rationale for a home game, but as an element of the show it just feels like a fairly pointless side trip that's afforded little gravitas.
Overall, though, even with my caveats the show is fun. It's a good time and a decent piece of fantasy media. If you aren't scared of animated breasts and can stomach the occasional musical number, give it a shot.
