A Battle.Net board member posted recently saying the user interface for Diablo III was "bulky" and "wasted space below the character".

He questioned whether the camera angle could be changed  and ...

Bashiok replied:

It's a fixed camera. Back when we announced the game we had our dialogue interaction set up where the camera would zoom in, and you'd see the characters up close and they'd talk to each other in this zoomed in view. We threw that out a long time ago though just because it was too intrusive, it stopped the game, pulled you out of the action, and just felt like too much. There was also a point where we zoomed in on the character in one of the videos to show some attack animations and item switches better, but that's not a feature of the game.

The camera doesn't zoom or tilt or rotate, it's a fixed camera.

It's kind of fun to watch people that have never played a Diablo game before, or it's been a long time. They immediately go for the WASD keys, and when those do nothing they then try holding down the right mouse button to rotate the camera. Sometimes by accident they're reminded it's click to move.

It's just not a control scheme and camera angle that are used a lot these days, there's maybe been a handful of games in the past five years that qualify as isometric arpg's? So anyway, props to all those games and the developers keeping the style alive. We're continuing the tradition, proudly, because we feel it's the best way to present a sequel in the Diablo franchise.

The Diablo franchise is known for the isometric fixed-camera style. Also, some of the terrain is only viewable at one angle and is made specifically for the fixed camera.