For me, an engaging storyline is the most important element of any adventure-style game, so huge props for a well-written story. My benchmark is my desire to know what happens to the characters after the end of the story, and I do!
The gameplay had a nice range from relatively simple to fairly difficult, but even the most difficult was doable within the context of the game.
While I suspected the nature of The Four Elements, I did not expect the twist at the end. At all. Really excellent game.