What do you think makes a good RP server?

From experience of running several servers and used to be staff on some top servers years ago, I would say it comes down to custom content and what your community wants if you ask them and try to come up with a content idea that no other server has. Than that will leave you more ahead compare to other servers, this can range from maps, cars, weapons, and addons basically.

Don't make another darkrp server...there's enough of them! we don't need more. Unless you are gonna code everything you self, don't do it.

events and good/charismatic leadership is what people flock to the most

I would say creativity, entertainment, and a good staff team. If your server is unique from all others and player's are entertained, and your staff team is competent enough to tell the difference from a hit and rdm then you should be on the right track! Just don't over-monetize your server with donation portals and VIP memberships.

A good server makes a well-coordinated work of the server team, gradually throwing in new ideas and concepts for the sake of good gameplay.

good community and good staff = a nice time. Also you need some nice addons and rules that make players like them.

A good server should give you pleasure in the game that would not break there were no bugs well optimized map!!

The Admins and Mods make up for 50% of the servers reputation, at least I think so. So they should be your main selling point.