I cannot believe that nobody has said this yet Diablo II: Diablerie. It has a lot of the things that 4th ed will have, and is also inspired by a blizzard videogame.
Talent Trees for the barbarian, amazon, and paladin just as there will be for Fighter/Ranger/Paladin in 4e
Special abilities that aren't used x times per day, but instead can be used over and over (make
a save each time you use it, when you fail it runs out)
Special abilities that are totally wuxia/video-game based for non magical characters (like the Amazon's ability to make arrows catch on fire, or split into multiple arrows mid-flight, etc)
A traditionally evil caster class as a hero class (Necromancer / Warlock)
Emphasis on kicking @$$ and doing super-kewl powerz over in depth role-playing or realism