The game is not that bad, i'd actually say it's better than classic D2
Is this acceptable, in your honest opinion? I mean, a sequel that's barely "better" (and that's very debatable) than the original release of it's 10+ year old predecessor?
Aside from that, the main flaw this game has imho is that loot itself is designed around the auction house. Unless you play only with self found items (very gratifying, i've heard, although your character will blow), you will always find yourself looking for upgrades in the auction house, simply because the loot system is so damn frustrating, that it leads you to it.
This kind of thing didn't happen in D2, where you found awesome mid-level loot that was perfectly viable for high level gameplay. The truly high-end gear was naturally hard to obtain, but what you could find on your own was simply so damn awesome that you could enjoy the game for years without having to resource to third party sites.This made the whole experience extremely rewarding, and it's precisely what D3 lacks, due to Blizzard willing to prey on people's frustration to make an easy buck with the auction house, something obscenely !@#$ed up, imo. Setting an auction house is ok, designing the loot system to revolve around it's usage is not, specially when real money is thrown into the mix. The RMAH being there to "protect" players from third party sites is a pretty story and all, but you have to be completely blind to not see it's true purpose. Otherwise, nobody would ever complain about the loot system sucking so bad as it does.
D3 lacks that feeling D2 had after a lot of polishing. Why the heck should such an anticipated sequel go back to barely "better" (again, debatable) than the original release of it's old prececessor? It doesn't make sense, and it is, i believe, the main reason why D3 has been such a disappointment for many people. The game is ok, but it definitely does not deserve the Diablo name. Heck, the only clear upgrade in this game is the graphics engine, and perhaps a few mechanics (healthglobes to minimize downtime, or the various class resource systems, for instance). That shouldn't happen to a franchise like Diablo. The game should be lightyears away from the masterpiece D2 is, but it failed to accomplish that objective.