If you want the full details… CLICK ME
The highlights:
- New Expansion coming, called Cataclysm
- New races for Horde (Goblin) and Alliance (Worgen)
- Level Cap raised to 85
- Skill caps raised another 75 points
- Lots of new zones in Azeroth, and mega changes to existing zones. (example, The Barrens will now be two zones)
- Goblin Racial: Rocket Jump / +1% to casting/attack speed / 15 to Alchemy / Personal Hobgoblin servant
- Worgen Racial: Don’t need a skinning knife to get leather / Sprint / Worgen Form / Reduced duration diseases and curses
- Goblin Classes: All but Paladin and Druid
- Worgen Classes: All but Shaman and Paladin
- Following Item Stats are gone: MP5, Spellpower, Defense, Attack Power, Armor Penetration
- Major Changes to: Haste and Block
- Reforging allows crafters to change stats on gear
- Big changes to Fishing
- No more spell ranks. Spell power increases as you level.
- Warlock shards no longer stored in bags
- New race/class combos… Say hi to the Dwarf Mage (back from Beta!)
There are some more bits of information here, but don’t take my word for it… See for yourself.
Oh, and they unveiled the Monk class for Diablo 3, but this is an MMO site, and I’m sure none of you are interested in that. 
Totally awesome!