I adore the graphics of the Mario-franchise. From the first to the current high-gen console games.. It might not be the most realistic stuff ever, but nothing makes me smile and enjoy myself quite as much as when I'm mashing a gamepad while looking at and playing that stuff. At least gaming-wise.
Best is definitely subjective. If you are looking for the most 'real' looking games, there are a few that come to mind (Crysis being one of them).
"Watch Dogs" looks pretty damn good. Check out the rain scene and the light reflections off of the wet road @ around 6:20.
Other games that I can think of: Splinter Cell (dem shadows), new Need for Speed games, Uncharted series, Skyrim, Battlefield 3 (especially the PC version), and the new Ghost Recon.
There are also other games which are not necessarily real, but have a unique artistic style. For example: Jet Set Radio, XIII, Viewtiful Joe, Many of the new DBZ fighters, Conkers BFD, Team Fortress series, Mirrors Edge, and many others.
I think you should change the title of this thread to "Most realistic" rather then "best." Just a thought.
final fantasy franchise, in all my games of them at their time they were stunning and just amazing, the metal gear solid series is very very nice too, i can still remember on metal gear 3 when you have the cut scene with EVA in the woods in some cave before one of the final missions