The original Guild Wars did pretty well, there was a decent amount of players and there was enough end game content to keep them occupied. GW works with a payment system different from WoW however. Instead of having to pay monthly fee's players only have to buy the game once to be able to play it infinitely in order to maintain income ArenaNet made different expansions. First there was Guild Wars Factions followed by Nightfall and finally there was Eye of the North, each expansion you could play withouth having any of it's predecessors. The problem with this system, in my opinion, was that it pulled players away from earlier expansions, the people who bought the expansions were mostly people who already got the most out of the world they were in. Players who didn't get the expansions would be left in a world which was now scarsely inhabited by others, after all most people would move on to the next world with all the cool new content.
Why did I talk about all that? Because GW 2 will have the same system as GW 1, you buy the game once and then you're free to play it as long as you like. Does this mean that there will be expansions again, with the same consequenses as it had on GW 1? I'm not quite sure. While it seems to be logical to assume the same system (and we're going in speculation mode here) ArenaNet could also use a different method, by making downloadable content for example, which add certain area's for players to explore. This is different from GW1 in that it doesn't drain the world of people who bought the DLC, because it would be just one area which is off limits to those who didn't buy the DLC. Imagine, it would stimulate trading of items that can be found in the DLC area and the people who wen't there would still be part of the orignal world.
That's it for this post, I didn't even mention anything of the content that's already confirmed. Guess I have a topic for my next post already :)