The atmosphere of cooperative truth-seeking, where it feels like ideas are taken seriously, there is a genuine effort to understand what others are saying, and frequent engagement with the least convenient world.
Also, awesome users like Eneasz for the HPMoR podcast, AdeleneDawner and PeerInfinity for the actually useful horoscopes, Vladimir Nesov and others for maintaining the wiki, Alicorn for her pony illustrations, jb55 and OneWhoFrogs for ebook versions of the sequences, BrandonReinhart for the examination of SIAI finances, and of course anyone who posts regularly. Since many of these kudos are for recent projects, I've sure I've left a lot out.
Recently I asked "What bothers you about Less Wrong?". It might be worth going back and checking out what people had to say, to see if there's something you can do to make Less Wrong more fun for everyone. (A few people made cool posts in response to complaints about lack of technical discussion, for instance.)
Let's hear the other side. What is cool about Less Wrong? What drew you in, what makes you stay, what makes you obsessively read every comment of every post? Is they're something we're doing right that we should be doing more? Bonus points for pointing out how we can make our awesome traits even more awesome, or how to make our awesomeness more obvious to outside folk who'd appreciate it. Whatever it is, add it to the comments.