Originally Posted by DArtagnan 
Biggest problem with the game is the itemization and skill system. The first has a very detrimental effect on your desire to keep up the loot hunt - and the second means you have little to no reason to replay the game.
Just about the two most vital features in Diablo - and they managed to mess them both up by relying on the inevitably short-term feedback through endless iterative testing.
Are you saying that they didn't playtest for multiple runs all the way to high level characters? They certainly had enough time.