Longevity?
Most people i know are in act 4, or have killed diablo already. In 2 weeks. That includes levelling. All the shitty MMOs that came out in the last 2 years lasted longer than that.
Just because the loot is super random, and 90% of the time you get crap a lvl 40 wouldnt even want, doesnt mean the game as 'longevity'.