Blizzard plays cash grab with a beloved franchise.
Punishingly low drop rates of the higher quality items are intended to facilitate a high demand of the Real Money Auction House. This completely destroyed the feeling of reward from defeating difficult mobs and bosses in the game. When you have to either grind tons of gold to buy from the Gold Auction House or shell out potential hundreds or even thousands of dolalrs it cheapens the experience and kills any feeling of progression.
In my 200 or so hours of playing the game (200 I wish I could take back) I can count on one hand the number of actual upgrades I found for my characters. This includes 2 classes at level 60 in inferno and a couple in Hell difficulty.
No end game. Blizzard expects players to grind the same content over and over. There isn't much variety here, and since Blizzard chose to release the game without pvp to get the game out of the doors quicker there is no reprieve from mind numbing grind.
The community is being almost completely ignored in Blizzard's forums and countless constructive posts ignored. It leaves the impression that we as players are being ignored and that Blizzard has our money and doesn't care what happens now.
In Blizzards effort to take a slice of the pie that gold sellers have had to them selfs for so long they introduced undesirable consequences that they will likely never choose to remedy.
So in closing. Blizzard may have sold millions of copies of Diablo 3. Don't let that one bit of information fool you. They have many years of good reputation and great games like Starcraft 1 and 2.
Diablo 3 has been one of their best selling games and I believe it is due to their great reputation of previous releases. However we now see so much disappointment from the community at large one wonders how much that reputation has suffered and if their sales in the future will suffer for it.