This game is actually one of the WORST PvP MMORPG's I've ever played. Its classes are totally unbalanced for one-on-one PvP and it seems mostly inhabited by semi-demented thirteen-year-olds who are more interested in being "Game Rats" (Much like a "Mall Rat" they hang out in Ironforge and verbally interact with each other or endlessly duel.) than actually playing the game.
The organized, multi-player PvP aspect itself is a simplistic and usually very disorganized "Captute-The-Flag". The One-on-One PvP consists largely of being ganked by those far over your level or a group of same. I've seldom seen a "fair" PvP encounter. There is an "Honor (Ranking) system)that rewards this behavior with no countervailing "Dishonor" system so it's open season on everyone.
While it does affect your individual rank and standing in the PvP community, PvP has absolutely NO effect on territorial game mechanics, "War" or no "War" between Alliance and Horde.
The dungeons (Instances) are the usual collection of uninspired killing grounds for the usual over-powered and over-populated NPCs. You do get some nice equipment there and mercifully they are mostly short encounters of a few hours at most.
In short: In my opinion the PvP aspect of game is only popular because it allows one to "legally" get away with darn near ANYTHING to the obvious delight of the immature clientelle. Don't believe me? Spend a few hours during "Prime Time" in Ironforge by the bank for an eye-opening experience!
The best that I can say about this game is that the developers kept things like corpse recovery and dungeon experiences short, probably to appeal to the limited attention spans of their target audience. Given the game's lack of content and lack of depth, had they been Everquest-like the game would have been a failure. IMO the only thing that accounts for its success is that there really was not a better MMORPG since DAOC and there isn't one in the pipeline for the forseeable future.