Dungeons and Dragons

I don't feel D&D hit its stride until 2e. 3e and 3.5 all had their advantages and could maintain the RP of 2e without too much handwaving. 4e's overhaul changed the core of 2e's success in favor of a weird, wargamey/ videogamey tone, but had individual good ideas. 5e is a flexible, perfect marriage.