This game came out of nowhere for me. I just started playing it based on something I read here and I have been having a blast. The foundry is especially good and has some great quests so far.
I have not done the instances or PvP yet so can't comment.
Also the game feels very very packed in every zone at all hours day and night.
As for the game being free? Well I have not purchased anything other than adding two char slots for 500 zen ($5.00)- I might add more bank slots and bag slots at some point. The game gives you more than enough for free.
There is a gambling aspect to this game I have seen with these nightmere lockboxes. The game makers must be making a fortune selling keys from their store.