There are tons of free MMOs out there but few, if any, have the amount of polish that you'll see in WoW. The good thing is that WoW is pretty old in terms of online games, so graphics and game play have come a long way since WoW's release.
I would recommend taste-testing a bunch of different games to find what you'll like best. A great place to start is Perfect World Games, they have software called ARC, which is a centralized software where you can download all the Perfect World games, similar to Steam. Perfect World has a good dozen free-to-Play MMOs that you can try. Since you are into WoW, I would recommend checking out Forsaken World first. If you are looking to stay in the Fantasy genre, then NeverWinter is also awesome.
Some games that were subscription based also changed to free-to-play, which might be more your alley. A couple are DDO (Dungeon and Dragons Online) and Lord of the Rings Online.
If you are gaming on a Mac, then DDO and Lord of the Rings Online are the way to go. Unfortunately there are few free-to-play options that are Mac compatible in the MMO world.
Hope this helps!