I played it quite a bit in the beta and it was a fair amount of fun, although not very deep. The quest system was very similar to WoW's system (guy with yellow marker over his head has a quest for you), and the combat was more involved then WoW, but it's definately not reflex or twitch based (just throwing that out there because in screenshots and videos it can look like a third person shooter, you have an autoaim that takes care of the shooting for you). One thing I liked was there were very few times where I had to grind to another level, and that was during the beta, so they've probably added a number of more quests, so you'll never have to grind a level. For me that is a great thing because I hate grinding levels.
Overall it was pretty fun, but I got tired of it after about a month (to be fair, I also only played WoW for a month, so I'm not exactly the best judge a MMO's longevity). Since it comes with one month of play, I'd say it's worth $20.