Crysis came out in 2007, and is still the best looking game to date.
The game didn't even max out the Crysis-engine...and there are plenty of mods that bump the graphics beyond the default-max Very High settings.
Not to mention that Crysis has "actual physics" (youtube 10,000 barrel explosion)...whereas in Left4Dead, most objects don't move...ie. Chairs, tables, and other small objects are basically a part of the map.
Hell, the Crysis engine is so graphically demanding that the Crysis2 engine is actually a downgrade so they can put it on consoles.
You can't compare the respectable Left4Dead engine (maybe a honda civic) with the awe-inspiring Crysis engine (more like a Lexus).