The best RP I've ever been in was called Rise of the Titans. It was a highschool-esque RP where a bunch of students branded together in an alternate Gotham to form a team of 'Teen Titans'. We as the players started from the ground up in a fairly reasonable and almost realistic manner. Though a lot of players dropped, those that remained formed a tight knit group and eventually we took the RP into a more original setting and left the DCU completely behind. 

There was a lot of wow moments such as playing a fake out of a character death and even having a villain discover the heroes' identities leading to a total storming of their base. 

I've tried to replicate the experience several times without luck but the original will forever hold a dear place in my heart.