config file is in /Documents/DeadIsland/out/Settings (open Video.scr with notepad):

Resolution(1920,1080)
Monitor(-1)
BPP(32)
FSAA(8)
TexBPP(32)
TextureQuality("High")
Filtering("AnisotropicTrilinear")
Fullscreen()
Shadows("High")
ShadowMapSize(2048)
SpotShadowMapSize(4096)
Lightmaps()
GammaFloat(1.20)
MaxRefresh(60)
MaterialQuality(0)
FXQuality(4)
FXFadeLevel(0)
WaterQuality(0)
GrassQuality(0)
EnvQuality("FullDynamic")
ShaderPath(5)
VSync()
PostProcess("Normal")
DisplayDeviceType(0,0.000000,1.000000,1.000000,1.000000)


change resolution, gammafloat and maxrefresh to your liking or leave them alone. Do NOT enter anything for fullscreen, lightmaps or vsync, simply having the entry enables them

if this config crashes your game then try changing shadowmapsize and spotshadowmapsize to 1024 and 2048 respectively