When Warhammer came out, I bought it and played the crap out of it. The game was so easy to play that I maxed out the lvl on 3 toons really quickly. But then, it all came down to PvP. The same zones over and over and over again. Didnt even last a year with that game and my disapointment over it was huge.
That being said, I seriously hope that they do NOT make this a PvP mindset game. Yes, I like PvP and want it in there. But I do not want the game based only around and with the concept of it being a PvP oriented game. Missions/quests, dungeons (or zones or instances or whatever you want to call them) need to be in there for some PvE gaming. Yes, I realize that Warhammer had PvE, but it was a joke.
I'm really really hoping that they learned something from the fantasy game and will make the 40k version so much better as the potential is there. Regardless though, I will buy it. I will play it. How long, depends on how well they do.