I always liked SWG's social aspects, such as the Entertainers/Medics healing your wounds in Cantinas/Med Centres (and equally important that they would heal over time unaided, but this was faster) and the way they had that "Master Training" thing where you could teach players the skills you knew. You then earned "Mentor" points (or whatever they called them) which you needed to get to the top of your profession.

Of course it fell down if you couldn't find a pupil but it was an interesting way of introducing a social aspect.

That and the sandbox economy fuelled by other players (in pre-FUBAR SWG the only equipment of note came from trade skills.)