I met so many awesome people in SWG. It did a really great job of fostering social interactions in a real way, not just transactional menu button presses. To get a lot of things done in the economy and the different aspects of the community you had to talk to people. You were also part of a persistent universe, so you could frequent the same spots and end up bumping into people.

Just those two aspects I believe are where online games have gone so wrong, and it's an easy fix. Persistent servers instead of matchmaking, and don't make every little interaction a gamified polished system. Leave some room for the chatbox/voice comms to be relevant for getting stuff done.