Countless stars that shine in the world of EQ.
EQ was challenging. Exp took time to get, kills cost you that precious exp, mobs could be trained on you, soloing was virtually nonexistent (save for a few classes), overall, you really had to work for what you got. This is what made the game so wonderful. Nothing was given to you. You had to put in time, effort, and energy which made the rewards all the more satisfying.
The world was also spectacular. Yeah, the graphics may be ancient by modern standards, but the world was huge and full of so many things that made you have to be on your game. Dying was bad; it cost you exp. As frustrating as this was, it made you become a better player, which made grouping all the more fun.
Lastly, the lore of the game was unmatched, even today. So many subtleties were in the game, like picking a deity, different vendor prices based on race or class, and things like that. These made the game fun, more interactive, and added a whole element to the experience that you just don't see in modern games.