(1) It's super bloated. It requires a 10x the resources of an old school PHP forum. I'm not saying an old school PHP forum is better. Only that gees! Why do I need to pay 1GIG dedicated machine when a shared PHP host was working for ~15yrs
(2) All the damn gamification that's so effing annoying. I've got enough notifications in my life. I don't need "You posted your first message", "You posted your first reply", "You edited your first message". The only notifications I want are those that are actually useful for me "You got a reply"
(3) Poor design for engagement. I have no data on this but I've never seen a discourse forum be as active as older non-discourse forums. Something about the way it's designed IMO discourages long lived lively topics. Where is the NeoGAF of discourse? Where is the Tigsource of discourse?