I would usually agree. However, if a game like Portal 2 is tagged at 30$, and offers less than 10 hours of play time, paying 55$ for a (pre-release) game that promises hundreds of hours at the very least is, well, a nice bargain. Because there is a LOT of content. And by a lot, I mean a lot. I'm sure you will be finding that you played for 400 hours and yet you still haven't entered some areas.
If you go by gameplay quality, you probably won't be disappointed. I have yet to see such fluid, fun and difficult gameplay in an online game as I saw in GW2. If you look at the graphics, yeah. 55$ might be a lot for a game that sports nice but not over-the-top graphics. However, the art is top quality and what is lacking in polygon count is made up by the sheer beauty of the world.
But yes, 55$ is a lot for any videogame, these days. I think it's justified (I haven't spent more than 20 on any videogame other than GW2 for ages), but you will have to see for yourself.