the sub fees value all comes down to how much content they give you per month or however often their content cycle will be.
I played (and payed) LOTRO for 2 years when it was still pay-to-play and felt like I was always getting my money's worth because of how much content the game had. ...and the expansions were only $20 each, for huge amounts of content.
and think about this people, this game will drop to $40-45 very soon, and like most MMO's, there are deals to be had with the sub fees. More than likely if you played this game for the next couple of years, you might only be paying an average of $8-10 per month, especially if they offer yearly subs.
I think that the success of this game and its sub fees come down to how much content they can provide. if the content is lacking, or unappealing, then this game will sink. but if the content is there, and steadily increses, you can bet your ass people are going to play the hell out of this MMO.