Without having really looked at Diablo III, I assume it will be similar to Diablo II.
Upgraded graphics and a new but similar storyline.

Anything Blizzard releases is competitive with other games, for Game of the Year on many sites.
So, D3 will likely be good for the masses, even if its nothing special for a lot of other users.

The whole game for me, was watching the character progress.
More along the lines of the talents...
I would always play around with a Trainer, to figure out where I wanted to end up.
And then play a character from scratch, without any cheats and try to end up somewhere near what I had with the Trainer.

Titan Quest, was similar to D2.
Except an updated graphics engine.
I'd imagine D3 will be similar to D2/TQ, etc...