If it changed a lot, fans will revolt and say it's not Diablo anymore. Titan Quest is still more innovative and in a way better, but what can I say I haven't experienced the Nightmare endgames yet. Hard to tell.
Brand name selling power. *sigh* Like I said. Disappointing day is disappointing. Don't get me wrong it's a really good game 8.5 from me, just not exceptional, revolutionary, one of a kind, or offering a vast enough experience that it blew my mind and I could forget about it being a rehash.
Lest we never http://www.gametrailers.com/video/modern-game-mega64/723924
Edit
Fixed link.