* [Any image] - NSFW
* [Any video] - NSFW
* [Topic worth discussing] - plenty of comments filled with ridicule and venom
Perhaps HN is where you go (from 4chan) when you reach a certain level of maturity?
EDIT: Obviously enough 4chan users here to produce a long and humorous list of our particular "strangeness". Before someone there decides I'm an enemy, I should state that I don't think they should be shut down, I don't hate them and I fully think they should be able to have their fun.
4chan is utterly brilliant, in a "you stay over there, far away from me, and someone else will actually visit you and find the quality posts and link me to them" sort of way :P
This history of 4chan is rather important to internet culture, really. 4chan came from a group of Something Awful Goons love affair with Japanese culture. It was were Anonymous were born, and where, over the years, said group became to be made of a three distinct factions - oldfags, newfags and direct action protesters. The difference between these groups is crucial to understanding a distinct group of security risks faced by internet connected systems today.
4chan has helped drive the discussion of the role of anonymity in online communities. It inadvertently raised the profile of stenography, due to it being used on images being posted to hide less savoury content. 4chan sparked such things as http://1d4chan.org which is a great repository of tabletop gaming culture. 4chan also helped to drive the evolution of many internet memes, especially image macros ('lolcats').
4chan is not without its problems, however. As hinted above, the anonymous image boards have always appealed to people wanting to exchange illicit images. The anonymous nature of the message boards does drive some (many?) of them to be, well, cesspits. The disparate groups that came together in Anonymous pull it in many different ways, causing tension and feuds.
So on second thoughts, let's not go to 4chan; It is a silly place. But I will be sad to see it go, and it deserves to be long remembered.
It is a piece of art as a service and and opinions vary about it wildly.
My 2c.