I have played both Flyff and Perfect World.
Flyff is fun at first, but it gets harder to level ._.
I'd grind for four hours and barely gain one level.
But I also played alone or with my partner.
If you can find a good party to join or someone to
level you, you can get pretty far.
Overall it is fun, but can be very laggy.
Perfect World was okay. I played with Celestay and Reanna.
The only problem is if you're playing with friends and they
choose one race and you choose another, you won't start
in the same place :\
It always took me forever to find my friends.