The Game Developers Conference is an annual gathering of video game developers which features, lectures, tutorials and other events related to game development for and by professional developers.
During the 2012 GDC, Christian Lichtner did a presentation on the Art of Diablo 3, going over Blizzard's and Diablo III's art philosophy and the development of many art aspects of the game, such as the evolution of Azmodan, Diablo and the various armor sets present in the game.
The presentation emphasized the core values that Blizzard has adapted to all of it's current franchises: stylization over realism, strong silhouettes, bold use of color and dynamic animations, all with the purpose of supporting the gameplay to the fullest.
Some of the core concepts that were kept from the original two games was in particular the classic isometric camera, which worked very well for the game. The fixed camera angle allowed them to design the world without having to account for multiple angles, giving higher fidelity graphics with less polygons.
In particular with the design of demons, it was very important to convey that they were demons and not just beasts, meaning intelligent and advanced to some extent. They wanted to convey that there was a hierarchy in Hell and some form of culture, and this is expressed mainly in the monster design with armor and clothes rather than the story itself.
In regards to weapons and armor, the stylised design is kept, but everything was made so that it could believably exist in some world. For instance, weapons and armor should be possible to be created in the real world, for instance by a cosplayer, to live up to this standard. Even the high-end gear, which is quite intricate, is intended to follow that pattern.
Armor sets themselves are also designed differently depending on whether they're intended for the late game or not. Early armor sets taht are acquired through progression are intended to change a lot as the player finds new gear, but not necessarily become successively more powerful in appearance. That is reserved for the late armor sets acquired in the game.
When designing Diablo himself, many concepts were scrapped along the way. The earliest designs were essentially an upgrade of the big, hulking beast Diablo seen in Diablo II. Though ultimately scrapped, the prominent shoulder-mouths seen in later versions were born here. Other versions focused even more on the bulk, while one incorporated wings into him for a more regal look, and even a snake version. The bulk couldn't really be applied to the game however, and more lean and sinister concepts were pursued instead.
They wanted the character to have lots of horned, spikes and sharp edges, feeling that it was what defined Diablo. The final design