i have been mainly sceptical about this game since i got to play it one stress test beta weekende, since the story and art direction did not really captivate me.
But i keep hearing about the stability and performance of the engine used in TESO and i think that alone will either make or break the game: i think it will be a huge success if they can replicate the stability of the game in large scale PvP battles on live servers.
I also think that this will hold true in general: if you can build a game on a solid engine that give you good performance and (technically) good gameplay you will do solid, whereas a poor engine and poor performance (e.g. as in SWTOR) will most likely break your game, even if you have great lore and what not