One part of it is the unchanging landscape of all of it. Warhammer online came closest to satisfying that itch, but partial free to play isn't free to play, and i'm not going to pay to play a game that has such low upper level population. In most MMOs, no matter how many bears you kill there will always be more bears...no matter how many times you win at Warsong Gulch, the enemy keeps coming back. I understand there being areas that are heavily fought over, but my God, please let them actually be fought over. Wintergrasp and Tol Barad are good....now do that with most of the major areas of the world. Nothing game breaking, but keeps that you can capture with your guild would be nice (as Warhammer was supposed to have, not sure offhand if it does or not).
I want to be able to have an impact on the world. Guess what, in Star Wars Galaxies, having a house that people could walk into or knowing that Jogosh the Bounty Hunter used armor I made for him was awesome. Coordinating attacks to take out enemy bases and blow them up was cool, as was fighting so hard to defend our base and turrets that our enemies had to pay a group operating out of Russia a bounty to destroy them. It was hectic, tense, and fun. Sure parts were grindy, but the immersion made it so the grind wasn't so bad. I do recall that weaponsmith and droid engineer were particularly grindy, but that's about all I recall about those professions.
Anyway, back to basics here, I'm not looking for a game that requires me to group up, or need friends to do stuff with (or to send stuff like a lot of facebook games). I want to be able to play and enjoy a world that I can have an impact on. Not saying I want no socialization, but why not let me effectively socialize with people I don't know. Finding customers in SWG was fun most of the time, and most of my guilds were people I never knew before the game (one such guild was so great that I followed its leader into WoW and a handful of other MMOs, and we're still good friends today, but I remember that I met him by chance on SWG). I want to have fun, not just a grindy, messy, waste of time.