Those Icewind Dale maps surely do not look handpainted. I suspect they're either pre-rendered and displayed as tiles or rendered at run-time in the engine (I don't know how old the game is). The old Planescape: Torment game was definitely created using pre-rendered tiles.

I suspect the same of the Sherwood ones...though some of those effects, like the clouds and atmospherics, vex me to a degree; not sure how they're done.
M