DarkRP is a non-serious gamemode. Quite the opposite. You can run a serious RP in DarkRP with some heavy modifications using the darkrpmodification addon. But they don't survive for very long. I'm not sure what serious roleplay servers are set in normal urban life. Most of them are HL2, some post-apocalyptic theme, etc.
Unless you're not talking about serious roleplay, in which case I think you're talking about the rules and types of content rather than type of roleplay. Fun fact: half of the currently running DarkRP servers are either run by children or have someone who is running it to make a profit, where both have no care for their community.
