Diablo 3 has undergone many, many system changes. Today, game director Jay Wilson has posted a load of upcoming system adjustments, mostly made to systems that have already been changed. A few prime examples include the complete removal of "identify item" scrolls -- characters handle that with a universal spell now -- a dedicated potion button, and Blizzard deciding to rename the Stone of Recall and "just call it what it is," namely "Town Portal."
Another big change, the Nephalem Cube and Cauldron of Jordan (both integral to the crafting system), have been removed from the game outright. According to Blizzard, the two items "detracted from the benefits of returning to town to sell items, salvage, craft, and interact with the townsfolk." It's a lot to take in, especially given how long fans have waited for Diablo 3 but, in Wilson's words, "no one will remember if the game is late, only if it's great."
Head over to the Diablo 3 site to read about these changes (and many others) in more detail.