Empires is great because of the impact that any player can have on the environment of the game and the feedback they get for it that really rewards people for what they do, even if it's modest rewards like being able to pick up a new skill for repairing somones tank. The community adds alot to this, somhow the fomat of empires allows people to pick up on the little things players do and commend (or harass) them for it.
It's the teamwork. Working together as a coordinated 5-man squad while also being a part of a larger organized team with a real player as commander. Commanding is itself an entire unique game within the game, but I won't say much more since I haven't done it in years. Also, a sense of combined-arms combat due to vehicles. Of course its a bit arcadey but that's where... comes in.
