The "linear scaling" feature on the EE only works on sprites, backgrounds always use nearest neighbor. Seeing how jagged the background looked when zoomed-in, I thought it was a bug but the description in the menu says linear scaling is only for "creatures and spells". So that's intentional for some reason. It also says that "nearest neighbor scaling is what the original game used". But I'm pretty sure that's false, there is no zoom feature or resolution options in the original, so any scaling is done by the gpu/display, not the game.
My only problem with the original game with the widescreen mod is having to choose between the native resolution of my display (1920x1080), which makes everything too small, or a lower resolution (like 1366x768), which ends up slightly blurry when scaled by the gpu. I was really hyped about the enhanced edition, but the linear scaling not working on backgrounds makes the zoom feature look even worse than running the original at a low resolution. And even if did work on backgrounds, why linear scaling??? It's the lowest quality algorithm, the same blurry garbage used by cheap displays. Why not cubic/lanczos/spline? At least as an option.