The question says it all, what changed from Diablo II to III?
closed as not constructive by Wikwocket, Sorean, Raven Dreamer♦ May 15 '12 at 19:22
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This site has the most comprehensive list.
Here are the largest changes:
Those are the core changes, please refer to the site for a more comprehensive list. I will work on this a bit more when I get home but I have to get back to work. :)