There are a lot of great things about this game and it's free, but this game allows you to level up too quickly and too often. Once you hit level 60 (this happens easily within 6-8 weeks of playing for around 2 hours a day), the entertainment value of this game diminishes quickly.
They keep adding more maps and features, but because there's really no character advancement after level 60, I don't see a point? You can get another character/class to level 60, but they go through the same adventures to get there. If you want a third or additional characters, they charge you. If you want to really compete in multi-player, count on paying for it.
When your character is already at level 60, I don't see the fun in grinding through additional scenarios (scenery and monsters may change, but the missions are pretty much still the same in the new modules) for an off chance you might find an extremely rare item worth using or selling at auction.
The graphics and performance are good if you have a GTX 560 or better and you're running at least an i3 with 3GHz or better. It's definitely a fun game for a couple of months though. And it's free!