Mechanics wise they offer a lot of enjoyment and for PC RTS games, the fanbase makes so many graphical mods that they can keep up alright with changing times. Then there's others that are made in isometric art with emphasis on cartoony/pixel which is hard to age.
3-D with cell-shade overlay has decent longevity as well such as Okami because it was stylistically done rather than realistic. Another good example is also WoW. The problem with striving for hyper realism is that the graphics for it can age really fast with advancements in lighting/shading/ect.
thats a good point Cereus. when you go for ultra-realizm, later on your graphics just look like shit. But, when you go cell shaded, cartoony, or very artsy, time doesnt really matter as much.
im hoping borderlands looks this good later on. Since it kinda took that approach.