Hi @pau, and welcome to the forum! 
Also thanks for leaving your feedback.
It’s generally true that people tend to write longer replies on forums. But it’s not a rule. Posts can be brief as well. Also Reddit and Facebook use somewhat the same format as Discourse (the forum software we use here). So I think people can adjust fine to it.
And about long threads, which do happen, Discourse has an option to summarize those. Saving people some time by just tuning in to what may be the most relevant comments. There are a ton of other features that help moderate and organize communication in a way that’s not doable in group chat.
Anyway, have look at the docs, there are some nice articles in there to get you up to speed on the forum features and whatnot. We also have a few community maintained wiki pages (you can also add one yourself).
Discourse can be heavily modified with themes, plugins and theme components. I’m using a few here, but I want to limit its use for stability/compatibility reasons.