I think another CoX feature that shouldn't be overlooked is the billions (trillions?) of combinations to customize the look of your character. I love the fact that we are free to be so creative with our looks. It has turned me into an altaholic.
I find it shocking that MMOs that started development after CoX's release still limit you to less than 200 possible combinations of looks, most of which look the same. I'm spoiled now. I can't play another MMO without getting angry that 1/12th of every character I meet has the same hair style I do (which is usually the most distinctive part of the customization). I know other MMOs expect that the gear will make characters looking different, but that fails when every min/maxer goes for the same epic dragon sword of eliteness.
I keep trying other MMOs, but I always come back to CoX. EQ? No, I can't stand the grind or politics or the loot obsession. EQ2? No, the graphics make me want to puke and I can't stand one more quest to kill a bunch of grays. WoW? No, I feel no compulsion to be pwned by a 12 year old. SWG? LOL, NO! Too many reasons. Vanguard? No, I want a game where bugs are fixed, content is added, and people play. Auto Assault? No, nobody else played.