Really good and interesting talk about engaging gameplay mechanics, and how changing existing mechanics can be good:

http://www.gdcvault.com/play/1015659/Realm-of-the-Counter-Intuitive

Pretty interesting. Thanks for sharing.

I played Realm of the Mad God after this presentation. Its a very intersting concept, but failed to keep me playing.
Perma-Death can be cruel, also I pretty much didn't find new items around and hated to not be able to sell anything. I'm conditioned to gather everything i find, and in this game you have to keep everything laying on the ground that's not for your class. Most items you do find are not for your class...