User Interface in Diablo 3

The UI is generally the same as its predecessor, besides the graphical upgrades, and will be very familiar to Diablo II players. However, there are some differences. The health and mana globes have moved more toward the center, rather than being all the way in the corners. The stamina bar has dissappeared. The experience bar is now at the bottom of the screen spanning the distance from the health globe to the mana globe. The UI is almost definitely not finalized so although it will probably resemble what we have seen so far, it is certainly due to change. 

Skill Bar

Above the experience bar, where the stamina bar, experience bar, and potion belt used to be, are where the skill and scroll slots are. There are four slots for keyboard activated skills, associated with the 1-4 number keys. They are followed by two scroll slots associated with the 5 and 6 number keys. Lastly on the skill bar are the mouse skills. There is a primary for the left mouse button and a secondary for the right mouse button. The secondary can be quickly switched back and forth with another skill by scrolling the mouse. The mini menu returns from Diablo II, but it does not appear to be collapsible. 

Buffs

Buffs and debuffs are now displayed on the HUD. They are located in the very bottom left hand corner of the screen and are represented with pictures similar to the skills in the skill bar. 

Mini Map

There is now a mini map displayed on the top of the right hand side of the screen. This replaces the translucent map overlay that was present in Diablo II. Your character is represented by a yellow circle. Allies, which include mercenaries and pets, are represented by purple circles. Orange circles indicate NPCs. Text displaying the current location is directly above the map. 

Inventory

The current build of Diablo III drops the old, grid based inventory system in favor of a new bag system. The player has three bags, one each for small, large and quest items that are represented as tabs in the inventory page. Each bag starts out with a limited number of slots but can be upgraded by the player, helping eliminate the need for the player to continually keep going back to town to deposit their items.

Skill Tree

The skill tree now uses illustrative icons similar to World of Warcraft. According to Blizzard, the coloured icons make it easier for the player to differentiate from the greater number of skills available in Diablo III as compared to the first two games.

Mini Combat Log

Things such as the damage you cause when you get a critical hit and when you block an attack with your shield will be displayed with small text that appears above enemies' heads. The text moves upward and quickly fades away. 

Enemy Health

Unlike Diablo II, enemies' health bars now appear directly above enemies heads instead of at the top of the screen. However, for Super Uniques and Bosses, there will be a separate health bar on top of the screen, staying there regardless of the location of the mouse until the enemy is destroyed.

Elixirs

Elixirs have been seen in the game as well, while in Diablo I they would give stat bonuses, there has been no official statement as to what functions they serve. However, it appears that they provide stat bonuses here as well, judging from the names matching with the types of stats in Diablo III. 
Elixir of Willpower I 
Elixir Of Vitality I 


Gems

Gems make a reappearance, and it appears that there is another type of categories of gems than their power levels (chipped, flawed, etc): prefixes such as square and star have been spotted. What they signify in item value and function is currently unknown.

Runes

Like in Diablo II, Diablo III has Runes, but they are completely different from their Diablo II counterparts. They now give bonuses to skills instead of items.