The big things are the inclusion of VRayRT and VRayRT/GPU. Previously, VRayRT was a separate product, that allowed for fast feedback as you tune your scene (here are a few movies made to demonstrate it). The new GPU enabled version can render 10 to 20 times faster if you have a newer supported video card for OpenCL/Cuda rendering (here's an older clip on youtube demonstrating GPU accelerated VRay rendering).
For VRay itself, at this point only a few features have been shown, so there are a lot of surprises still to come. But, here's what we've seen so far:
VRay Lens Effects - for glows and blooms. In the past you may have noticed pixelization in highlights from strong light sources. Now you can create automatic bloom/glare from these, for a much more realistic result.
VRayDistanceTex - a new material that allows you to use ambient occlusion type effects on surfaces with displacement or fur - an effect nor previously possible. This allows you to reduce local displacement near objects sitting on a surface to create a snowfall effect, for example.
VRay Exposure control - a new entry in your Effects rollout to apply VRay exposure to max standard cameras.
Dispersion - get physically accurate prismatic effects in your caustics or other refracted light.
Stereoscopic shademap caching - much faster renders for when you need both left and right eye renderings.