The microtransaction model is fine and actually quite excellent if done right -- see Path of Exile, for example. GW2's problems have nothing to do with its economic model; in fact, its economic model is what has saved it from being a resounding failure and instead kept it merely underperforming.
This game is not very good and would have been as much of a trainwreck as SWTOR if ANet had gone with a subscription model. Bad gameplay, poor design and insufficient progression content is what has made this game an underwhelming flash in the pan. They dropped the ball in the development phase and never really picked it back up.