I have played both the original and one of the latest "illegal" iteration. I have to admit that the amount of socializing you can find on those servers makes the current wow feel sad. It brings back that feeling of "having to group with others to do it right", that's something that is missing from today's game selection, although not everyone is fond of it.
What I feel is not there anymore is the exploration, the unknown, the cool item you would not have expected. You can play on one of these servers and have fun leveling to 60, make friends and re-experience something nice, but when you hit cap it's all about BiS farming and doing it in the most efficient way. It is as if there is a crowd of players who constantly move from one of these servers to the next, only to see how fast they can level up, get their bis gear fro mdungeons and clear all raid content available.
I couldn't find the feeling I had in 2004 about end game dungeons.