I didn't get too much into the online modes, but it was fun when I wasn't completely outclassed. Weapon fusing was also a neat idea, though I stopped combining weapons after awhile.
Intensity levels were one of the most novel things about the game; I think that could easily catch on.
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http://img812.imageshack.us/img812/3492/eponaharr.jpg
Nominate SuperNiceDog's Guru-choice, then Epona.