SimCity 4's Graphics Engine
I found this discussion of SimCity 4's graphics engine very interesting. Apparently SC4 is the first version to go with a truly 3D polygonal geometry, though for a variety of reasons discussed in the article they limit the view angles for highest quality and speed. I also found their analysis on the last page that current graphics technology is far better suited to first-person games than god-games like SimCity pretty interesting. Makes sense especially since an FP perspective naturally limits the amount of geometry that must be rendered in high detail.