Metro Last Light requires about 5 TFLOPS of graphics performance to play with maximum graphics at 1920×1080 and maintaining 60fps. See the page on game performance.
The 4A Games proprietary 4A Engine makes this game about as demanding as Metro 2033.
SETTINGS: DX11, Very High, AF 16x, motion blur, SSAA, Tessellation very high, PhysX,
COMPARATIVE GPU PERFORMANCE CHART
See the page that features a graph of the relative performance of video cards.