Maybe it is more than an instance. Maybe it is an idea, a world-historical vanguard, light itself. 
actual attempt to answer (cringe)
We’ve been around for three years on a lemmy fork before federation. The lack of federation for years as well as the place we splintered off from (/r/chapotraphouse) already having a unique microculture within Reddit has given this instance, in my opinion, a distinct culture compared to general-purpose and even other hobbyist instances.
Regarding specifics, Hexbear is a vehemently queer-friendly/intersectional anti-sectarian socialist instance. Check us out 
Hexbear is a billion times better than the general population about vegan and covid conscious stuff. I can’t forget this. Everyone always harps on this place being safe for queer people. But I can’t get over the number of left spaces that fell apart because the admins needed “vegan hate stirring #4 this week”.
This blood mouth loves their vegan comrades
Borger time
And it’s very much appreciated from the otherkin community. When you live as a nonhuman, you become acutely aware of the fact that 95% of people are human supremacists and think your life isn’t worth protecting because you’re an “inferior species”. Cue the old “if they want to identify as animals they should be eaten like animals”. Carnists are fascists and this is the rare non fascist community.
Environmental stuff in general
Been a long time since I’ve been in a place where “climate activists fly on private jets so I’ll continue to not feel bad about my open air coal burning facility” hasn’t been a zinger
Vegan socialist here, is hexbear an openly vegan space? I’d love to join a popular leftist instance that is strongly against animal exploitation and slaughter.
Fully vegan? Nah sadly. Although our local vegan community is strong and outspoken. Also a significant amount of admins and devs are vegan. So there are clear rules about non vegans doing shit stirring. Granted, we’re not allowed to post vegan stuff outside of the vegan comm. Basically the non-vegans and vegans have well enforced rules of respect for each other. It’s not 100% ideal, but it’s the best I’ve seen in leftist, not explicitly vegan spaces. I’m thinking of a lot of those left Facebook spaces where admins would just post stuff like “well I’m just criticising white veganism”, all the while leaving space open for the whole community to bash veganism in the comments.
I like it here, and I think you’d like it here, but this place isn’t fully vegan.