I just beat the game on Normal at a leisurely pace, not spoiling myself with any information that would change my experience.
In all honesty, like many have said here, it is hard to think of it as a true sequel to Diablo 2. This comes as a real shock for me, considering that I thought Starcraft 2 was handled exceptionally well.
Don't get me wrong, the game would definitely appeal to those who haven't sunk some serious time into the first two games. Unfortunately, since I have and despite trying to go into the game with an open mind, I didn't find it very satisfying.
There are many turn offs that have been complained about ad nausem. Always online, auction house, unstable servers, errors, lag spikes, drop outs, skill system, normal is too easy, etc and they are all legitimate complaints.
What bothers me is that even if some of those kinks were ironed out, this game doesn't 'feel' like a Diablo game. There is something fundamentally wrong with allowing the player to hotswap skills whenever they want. It really kills the uniqueness of your character, short of the gear you've managed to acquire.
Being that all classes are designed to function on their own quite well, group dynamics are almost completely lost. I feel as if once I have found the right combination of skills, my teammates are only used to down monsters faster. Mind you, I haven't played much of Nightmare (thankfully, the difficulty seems to have been brought up to a tolerable level) so I'm not sure if my class will start feeling truly vulnerable at a later point. Here's to hoping that it will become more vulnerable and other classes will start to show their true value eventually.
Speaking of vulnerability, I'm finding it unnerving to play with a Hardcore character. Not because of the tension that is associated with dying, more of the tension associated with the servers being a mess, allowing me to die easier. It has happened once already. I got a Monk to a respectable level, I port into a quest zone and I get killed by a wandering elite I didn't even get to see until it killed me. Lag? Glitch? Doesn't matter. There's a difference between dying due to my own incompetence and dying due to server incompetence. I'm not going to climb the risky ladder only to be bullshitted out of progress.
The problem with Diablo 3 is that it can't be looked at as its own game, not with that magical 3 in the title. If it was, I don't think it would be as well received because beneath the brand loyalty, the game is surprisingly shallow and bland. It's a damn shame, because the artwork and sound design are absolutely phenomenal (as is usually the case with Blizzard). The plot and gameplay, while functional are just that: functional. Diablo 2 was not a perfect game by any means, but for its time it was exceptional. Diablo 3 is not terrible but I imagine that it wont have the staying power of the previous title... Just a hunch.