The Diablo 3 beta dates will be announced soon; release date is TBA.
Check out the gameplay video from Diablo 3, which shows a lot of promise. The footage was captured from the first ever Diablo 3 media/press event held on July 27th.
Diablo 3 will feature a persistent internet connection for authentication as well as playing online, although, it does feature a lot of new improvements which you can check out here. The Diablo 3 beta dates will be announced soon; release date is TBA.