My problem with WoW is that it feels like your character is on rails. Nothing you do seems to influence the environment, NPCs, or other players in a meaningful way. When you kill a player in PVP, they turn into a ghost, and then resurrect without penalty.
There is no incentive to WPVP in WoW. You can't take over towns or cities--because there are no mechanisms that permit it--and guards just keep on "magically" respawning until players get bored and leave. You can't even talk to opposing factions--which I think is a mistake. If players were allowed to talk to opposing factions, then that would faciliate all sorts of interesting stuff like diplomacy, deception, drama, etc. I guess what it boils down to is in WoW there are too many rules. Let the players make the (majority) of the rules, not the developers. A cool idea would be to allow the faction that controls a territory the power to shape rules or laws. Or maybe give players the power to control guard routes or something along those lines.
Then there are Battlegrounds where players are matched up in instances that are separated from the static world and given the exact same objectives over and over again--and at the end of the match--nothing happens. You're awarded points, and then you queue up again. You winning or losing has no impact on the persistent world. Besides the points you earn, it's as though the match never happened. It's boring.
One last thing that bugs me is how weak the penalty for dying is. Imagine playing Super Mario 3 or Morrowind with infinite lives or invulernability. At a certain point you start to wonder, what's the point? When my character dies in WoW, I don't care, at all--and that bugs me.
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I just hope you (Bethesda) learn from Blizzard's mistakes with WoW. You may not see these gameplay decisions as mistakes though...