I know I haven't touched much on this, because I honestly haven't done it very much. I gave it my first real attempt (outside of sitting in the keep a couple weeks ago alt tabbed "farming" honor and arena points) a couple nights ago, and the first impression was not a good one. It has potential, but if I had to sum it up in one word right now it would be "confusion".
I mean, I know what the end goal is, because i sat in the keep: Use siege vehicles to knock down the keep door inside. But I guess it just gets confusing for a new player to understand how you actually accomplish that. There doesn't really seem to be a set stream of clearly defined objectives and goals. When I went to the zone a couple nights ago, I ran up to what looked like a point of interest, which was a big building that looked somewhat important.
Ok, cool. Then I proceeded to get gangraped by about 50 alliance, and get stuck in a never ending cycle of being graveyard camped by 50 more people and siege weapons. Not so cool. I saw that you're going to change the GYs to be higher up in elevation, and then hopefully flying mounts will be completed disabled in that zone.
So after finally managing to run my corpse away from the zerg, and go back to my body and res, I hearthed out. That was pretty much the extent of my experience.
On another note, I've been playing the Warhammer online beta quite a bit since Sunday, and while the PvE content and much of the game is very unpolished, I must say that I absolutely love the fact that you can level up at a pretty decent rate completely via pvp and battlegrounds (called scenarios in their terms). You can pick up a bunch of repeatable quests, queue from anywhere you are via a button on the minimap, and fight the scenario for each little zone you quest in.
It's cool because in between queues you are doing quests in PvP zones, and you gain experience, money, and loot from killing players, as well as being rewarded for doing quests in those areas. Then, when the queue pops, you get to go play out a 10 minute battleground where you earn even more experience, money, and loot.
The public quest system in the game is pretty cool too. I'm not sure how familiar you are with the mechanics in that game, but it scores a ton of points in my book by putting heavy emphasis on not just letting, but rewarding players for heavy participation in world pvp and battlegrounds while they level. It doesn't interrupt the leveling process, because killing players nets you the same thing killing mobs would. You don't actually loot the players' items, but you at least are rewarded in several ways for pvping.
As an example: I logged out monday night after almost reaching level 12. I log in last night, start running to the next, higher level area, and on the way, I get jumped by someone my level. I turn around and slit his throat (I'm playing a witch elf), and it was a decent enough chunk of exp to level me up. I gained a level, by killing another player. How freaking cool is that??
The PvE content obviously will never touch WoWs, but their PvP system does honestly deserve a glance. It would totally kick ass if wow had a system like that, because I enjoy wow's combat better than I do Warhammers.