Free and Great never went together until now...
This game is new and not without its problems: latency and server issues which are improving on a weekly basis, content/instance repetition can be tedious to some, there are only so many maps and quests tend to get you playing a half dozen maps over and over until you get to the next episode.
There's also no world to explore, you're in 1 town and then you travel by boat to various instanced dungeons and environments.
Are these down-sides? Not really, it's free...and the gameplay rocks. It won't suck the life out of you like other MMOs.