Just installed it. It's much, much faster than the 1.X branch. A significant improve on speed on all modules.
The retouch tools are very cool but you can't, for instance, dodge and burn individual channels, which is a must for me. If I had that I'd never use Photoshop again! I like the small 1:1 preview window too.
The good side of not using Photoshop anymore is that you can do all the workflow over RAW images. You don't need gigantic 16-bit TIFFs anymore.