The lack of a customizable field-of-view is understandably a sticking point for certain PC gamers. It was no surprise, then, to see a big release like Metro: Last Light take some heat for not having a FOV slider. Today, an update went out on Steam that allows for FOV customization -- adjust the "r_base_fov" attribute in %LOCALAPPDATA%\4A Games\Metro LL\ -- and fixes issues with AMD hardware while also offering improved performance.
According to publisher Deep Silver, "The main reason for maintaining a fixed FOV is because we have 3D elements like the watch and weapon ammo that need to remain visible. Changing the FOV would break all the cut-scenes and animations -- you would be able to see inside Artyom's arms, or they would appear to float in the air in front of you. Or worse."
With all that said, expect a little funkiness depending on how far you take your FOV.