Far as graphics go, one of the most fascinating things to vee is water.
During the ultra-photorealistic push water evaded us, leaving most game devs to choose one of about half a dozen ways to simulate it artistically with a combination of transparencies, shaders, and reflections.
Even now, how games do water is still largely an artistic choice because the way we do graphics just doesn't handle the concept of "Moving, semi-transparent, refracting, non-normal, non-tessellating mesh"