What dear Chrysomallos was explaining is, in short, the aspect ratio of your game's resolution is recommended to be the same as your screen's native resolution, otherwise stretching occurs and most often this is the reason lower-than-native resolutions look bad/funny, as it might break the textures that are already scaled/stretched by game engine to match the selected aspect ratio. Going down from 1920x1080, suitable resolutions would be 1600x900, 1366x768 and 1280x720.

//Aspect ratio for those is 16:9, for the reference.