Diablo is known for having a small amount of classes, the first game having three, and the second having five. Seven in the expansion. Small, but the amount of builds possible for any given class are in the extremes.
Blizzard’s Bashiok talked about the class balance, and said that all classes are equally DPS classes. Meaning they are all capable of doling out huge amounts of damage equally. It doesn’t mean that a spellcaster who focuses on defense will be as viable as a barbarian who can tank bosses however.
In Diablo 2, the masters of damage were either Hammerdins or Sorceresses pre-expansion. One capable of mountains of physical damage and the other able to literally cover the entire playing field in blazing fire and fire-spitting hydra, which dealt hundreds, even thousands of damage every second. Each class had its role, but it was clear some were far better than others.
One part of Diablo 2 was the endless hunt for Cruel Greatswords and other incredibly powerful magic weapons. Monsters slain by the legion on Hell runs, and bosses being crushed underfoot by level 100 adventurers.
Blizzard has revealed some information on their item system. In Diablo 2, all crafting and etcetera was done via the artifact called the Horadric Cube. Finding out the exact specifications for an item however was incredibly difficult and needed mountains of experimentation and luck.
One difference in Diablo 2 is that items can no longer be upgraded to the next tier. That bastard sword will never become a greatsword. Like it? Too bad, hope the extra attack power isn’t too big a deal.
However, they can be salvaged for crafting materials or sold instead, which contributes towards higher-tier weaponry indirectly. Any enhancements that can be made on a weapon however are limited to adding sockets and enhancements. This is still an awesome deal however, especially since gems are easily upgradeable.
How they will be upgraded exactly hasn’t been revealed yet. It could follow the same idea as the Horadric Cube from Diablo 2, as a Cube has been confirmed as being in the game.
Because Diablo 3 uses a 3D graphics engine, customizations of appearances are far easier to design and create. There was virtually zero customization of purely cosmetic looks in the previous Diablo games unless you wanted to do some hex editing. Armor looks will be customizable without causing any stats on it to change. This is quite welcome as I personally got tired of looking at my sorceress’ golden fullplate.
Items will also have visual sets. They haven’t decided how these sets will appear yet, but Blizzard pitched an example of sets 1-5 appearing in Normal difficulty, and 6-10 appearing in Nightmare difficulty and so on. Diablo already has an extremely wide range of items.
Diablo 1 and Diablo 2’s extreme popularity have resulted in Diablo 3 becoming a bestseller through preorders alone. Blizzard has huge boots to fill on their fan’s expectations. Hopefully they will not disappoint.