I played most of the races just to see their different areas and feel what it was like to grow up there. Barbarians in the frozen north, wood elves in the misty forest of giant trees. It was such a huge world, especially for the time, you could just explore for days. And it was really well designed with interesting hidden stuff that kept you finding new things all the time if you wandered about. Each area had cute little decorations and context and NPC's related to the stuff going on in that area, with lots of hints of stuff you would see at higher levels and hints about the history of the game world.
It was a whole alternate universe you could dive into and run around in for hours. A lot of the magic of that was because it was so open. There were basically no keys or doors in the entire game. You could go anywhere, and players of various levels did mix quite often. It's the most perfect execution I've ever seen of a game where your level is the "key" to various areas. You could go to the hardest dungeons right away if you want, you're just going to die quickly. Even at low levels you could cast invisibility and go on a risky raid into high level dungeons to check things out and it was fascinating and terrifying hoping your invisibility wouldn't wear off. One of the great hurdles early on was trying to make the run from Freeport to Qeynos at low level, you'd beg someone to give you fleet feet and invisibility so you could get past the minotaurs and beholders in the mountain pass.
Of course a lot of the fun came from having other people in it. Even if you were solo'ing you could discover new things and then talk to your friends and be like "man have you seen this!?". I haven't really played WoW but I feel like it has ruined the things I really loved about the game; I liked not knowing the right place to be or the right item to get, I didn't really like the sitting around power leveling; I liked the fear of dying and having it be a really singificant disaster; I liked that it took some effort to explore and get away from other players who were overcrowding the most ideal power leveling spots and all camping for the same item.
There are a few games in my life that really stick with me to this day. "Faery Tale" on the Amiga was one. It was very similar in that it was a huge open world you could explore, with neat special places, and odd magical fairy tale stuff, like blowing the shell to ride the turtle. Another was "Out of this World" / "Another World". The gameplay was pretty shitty, but the art style was just so cool, and the universe was strange and gorgeous, it was like the Half Life 2 of that era.