Nothing advanced at all.
At most, its a variant of rim lighting, but considering how outdated the graphics look, I doubt that's what they were using (All though, this may give quite nice results)
More than likely, its probably just prebaked into the textures (could be a specularity map) during art design, nothing fancy. Alternatively, if you like that effect, but don't want have to make the textures, you could use a toon shader.
Microsoft (XNA) has very nice examples of the methods I described above
Also, if you REALLY want it to look pixelated, just make your mesh, and look for an example of how to generate voxels from a triangular mesh. If you really wanna get fancy, you could also program your application to remap the textures of the original model to the voxels