%LOCALAPPDATA%\4A Games\Metro LL\
In some multi-monitor systems there might be issues with selecting different resolutions than the default (native?) one. To fix this you can force the game to run in borderless windowed mode with an external tool.
In general advanced PhysX causes major issues. If you go into a fight in front of the church and FPS drops under 30 turn advanced PhysX off in the user.cfg
1. Go to %LOCALAPPDATA%\4A Games\Metro LL\ and open user.cfg with text editor.
2. Locate lines
and change values to your desired resolution.
On multi-core machines running on Win7, core parking can cause problems. The easiest way to disable core parking is to run this Disable Core Parking Utility and follow the instructions on the page.
At the pause menu under "game options" uncheck the "Enhanced PhysX" box. You will be required to restart the application after doing this action for changes to take effect.
Install the Metro: Last Light mouse fix.