It will be a lot tougher to succeed GW2 than it was with GW.
Oppositely to the general understanding, suceeding in a MMO is generally easier if you start small and end up big, rather than start big.
No MMO escapes this rule. One of the biggest success story of our time is LoL, which started small and end up big. They had time to change their game, adapt their infrastructure so it welcomes more and more players (Eve online another, smaller though, example).
GW2, SWTOR, Rift, TSW all launch very big, bringing players' expectation way too high by promising too much. When reality hit the fan, you have lost 60/70% of your playerbase. GW2 will take less risk as it's a no subscription game. So as long as you sold the game you win (which generally places the global cost of the game way lower, and thus the profit way higher), when in standard MMO selling the game is nowhere close to a victory, it's just the beginning of the journey.
GW2 won't be the WoW killer, neither will TSW. The very fact that you have to preorder the game to do the beta enlights it

. ArenaNet won't take the risk to make it test by people who may buy the game (see above why).
Wait and see, I myself preordered SWTOR and regretted pretty hard, never ever again I'll preorder a MMO. Those ones are generally way better 6 months/1 year post release.