The demo starts in a cave. You have multiple aesthetic class choices. There are customization presets. The sorceress has two female avatar options.
Barbarian skills: Rallying Cry, Unstoppable (23% increased speed and reduced damage plus fury), Leap
Fenzy and Upheavel requires dual wield or two-handers
Skewer requires two-handed slashing weapon
Cool down resets 10-second cooldown
Wrath of Berserker (every 20 fury you spend increases the effects by 65%)
Berserking increases damage by 25% and movement by 30%
Skill categories:
Basic
Fury
Defensive
Brawling
Weapon mastery
Ultimate
Source: IGN.com Diablo 4 First Hands-On Preview: Impressions from the BlizzCon Build