let me start by saying that everything is a matter of opinion...and I don't know how much my opinion is worth since I am 1. a hardcore mac addict and 2. I love video games but can hardly hold the mantle of gamer as I don't engulf myself as like what I think a true gamer does, that said...
WoW is totally awesome, it has a bit of everything for everyone in my opinion, challenging yet playable to the novice, battle, actions, great graphics, interactive enviorment, constantly evolving, it has RPG aspect, decent support and again, in my opinion, highly addictive.
I tried that free trial for 30 days (look the internet for it, its out there, but it is before burning crusade expansion so you wont have some of the new charries) but it will give you a good feel for the game to play for a while. Get ready for a long download, took forever and like a previous post said, it is followed by several updates.
it runs great on my mac and I have not even done any of the adjustments that a lot of people rave about (I will just have not gotten around to it and FYI, you can find those on the internet as well, some even on this very forum)
For the record I am playing on a black macbook. Standard specs: 2.0GHz Intel Core 2 Duo 1GB/120GB/SuperDrive