The real-time GI is amazing. Ray tracing is going to be a game changer, not only in terms of visual quality, but also because it's one of those rare times in computer graphics where the more advanced solution is actually making it easier on graphics programmers by replacing a bag of dirty tricks with a unified, physically based solution.

One interesting note: they say the GI is "instant" but you can actually see that they are using temporal stabilization to achieve this effect, and there's a slight lag between when the light changes and when the GI finds its resting point. I suspect removing this lag will be one of the things which makes graphics feel "next gen" when GPUs can handle enough rays per pixel to handle GI in one or two frames instead of a few dozen.