GLQuakePlus makes the following improvements to GLQuake:

Mouse look always on
Prevents illegal window height values when no height is specified
Crosshairs set on by default
Mipmap filtering set to trilinear by default
Water warp made more subtle to reduce tearing at boundaries
Stopped culling of entities when not beyond edge of screen
Shadows only applied to entity models (supports Quake, official add-on packs and Malice)

The Launcher allows control of the following parameters:

Fullscreen or window rendering
Screen size and bit depth
Brightness
Shadow rendering
Water transparency
Executable to launch: GLQuakePlus, GLQuake or WinQuake
Pak file to launch: Quake or a variety of other popular games/mods