Well, it depends a lot on your class and specc, if you can really have fun in PvP. The balance at the moment is..... well, shit. With my Arms Warrior i can have a lot of fun. But only with a pocket healer. Without it, i'm literally just a damage bot who can do nothing at all if half decently cc'ed and i will die in seconds because of none existing proper defenses.
With my destruction warlock, most melee can train me quite easily and there is not much i can do. Its somewhat doable if there is only one, but mostly, there are way way more on my ass. Of course you can have fun, if they not notice you. But as soon as the first big fat Chaos Bolt is seen, the fuckers turn on you!
So, well, not that fun or at least depending on circumstances.
Of course there is also Arena, but Arena is so unbelievable boring to me, i can't do more than absolutely necessary.