Blizzard Diablo Partners and content creators were invited to a Diablo IV preview which lasted one week with 3 classes available for play. Today, the NDA has been lifted, and here are some gameplay videos with first impressions.
Classes available for play were Barbarian, Sorceress, and Rogue. The content available for testing was up to Level 25. The Endgame Beta is still ongoing with NDA.
Dbrunski
Rhykker
ForceGaming
DreamcastGuy
Source: Reddit