Since the Voxelstein3D guys implemented path tracing, the engine produces some really cool and natural looking images:
The realistic path traced lighting may not be that obvious from these shots, but if you would replace the path tracing with direct lighting you'll get the usual hard shadows and there won't be a gradual lighting fall off in indirectly lit areas. It's a little disheartening that the voxels still look quite rough and create a stair stepping effect. I hope we'll soon have a free polygon based game engine supporting path tracing, the Brigade engine (by Jacco Bikker and Dietger van Antwerpen, IGAD) and Nvidia's OptiX being two serious candidates. You could theoretically re-use the geometry of an existing game(let's say Half-Life 2), apply some realistic brdf materials and render a photorealistic scene with real-time (interactive) global illumination.