Here are all of the current videos nVidia has done showcasing gaming on the SHIELD. I only included the ones showcasing Android gaming, and not the PC streaming ones.

The above is a comparison, but felt it was good stuff.

That's what they have up so far. I've played the boxing game on Tegra 3, and it's impressive. I can't wait to see it on Tegra 4. All of these games look impressive. It just goes to show how much highly optimized software matters when you have capable hardware.