I am experienced in Diablo & Diablo 2. I completed Diablo 3 Normal mode.

I can't help but feel something is missing in Diablo 3. However, ppl who never played Diablo before might like this a lot.
Overall, I have mixed feeling with this game.

Story:
It is a bit rushed. I dun understand how Leah's father is Diablo. You mean her mother has s e x with a giant red demon???
Also, Tyrael looks bad, like an old Mexican... lol. At least make him look legendary face, like Qui Gon Jin in Star Wars.
The final Prime Evil feels stupid in the story. I never knew evil demon can be so dumb.
Very lacked of NPC development and story, perhaps it is because I am accustomed to Warcraft story.

Gameplay:
I like the skill animation. Enemy difficulty is pretty ok. Nightmare mode is interesting when running with friends.
Depth of the gameplay is a bit shallow for me. Diablo 2 gameplay is more detailed, allowing user to customize different build.
Why they take out the talent tree??? These can make the game more interesting and allow ppl to sell their characters in RMAH.
The D3 world is too small. Too linear. I expect side quests and as we progress to higher difficulty level, new areas are uunlocked.

Graphic:
Initially it feels weird. After a while, I think it is definitely more artistic than Diablo 2. But no more gothic horror feel.
Overall this direction is still acceptable for me.

D3 is not comparable to MMORPG like World of Warcraft.
Blizzard can make D3 shines out much more by adding better RPG & MMORPG elements in the game.

For example:
Build real cities like Dragon Age 1. Allow side quests. This builds up story in Sanctuary
and the ppl living in it. They could have done this by following some aspect of World of Warcraft.
Players will venture outside the city surrounding region to quests and fight bosses.
Also builds up story for Followers. This bumps up the longevity of the game.
In WoW, the game can lasts for a few years!

Give character statistics to play around.
Give them the option to tweak the face they want. Dun want everyone look like old man... lol
Maybe also allow Fallout type of traits they can take during character development.
E.g. someone choose trait that at night, he/she improved accuracy of hit?

The auction house looks and performed ok. But do we really need to exit the game to go to Auction House?
Why dun access it during game at city?