Resident Evil 4
Quitting
In order to quit the game, you must press alt + f4 or go to to the menu, not the map/inventory screen. Once there, you must hit 'RETRY or LOAD', then 'RESET GAME.' This brings you back to the title screen so that you can quit the game.
Tweaks
There are very limited options in the game, but it has surprisingly good controller support that simply works without any configurations. There are a few tweakable parameters in the SetupTool.ini file which resides in the install directory.
SetupTool.ini
Resolution
Under the [SCREEN] section of the config file, there are SizeX and SizeY values, which correspond to resolutionWidth and resolutionHeight. For example if you want the game to run at 1920x1080, set them to:
sizeX=1920 sizeY=1080
Controls
There is a slew of gamepad and keyboard configuration settings in here which you can set.
Mods
There are many mods and texture enhancement mods available for download to improve the visuals of this aging gem.
Resident Evil 4 PC Texture Pack 2.0
This is a sizable effort of love with a couple gigs of higher resolution textures that improve the entire game. It can be downloaded from The Pirate Bay.
Enhanced Environment
Cerberus84 from ModDB has made texture pack which improves upon the default textures included with the game and can be downloaded from modDB.
Enb Series
The prolific Boris Vorontsov has a lighting/graphical patch available which greatly improves how the game looks, though it may decrease performance in some cases. You can get it from his site.