When reading game reviews, I have come across mention of a given game's "art direction" making up for a particular system's limitations, to give an example.
What is this "Art Direction" of which they speak?
In my opinion, it's trying not to break the immersion factor and to make the world believable. The Uncanny Valley has a lot to do with this...
If you look at the Mafia 2 trailer for example
http://www.zoopy.com/video/y8o/mafia-ii-e3-2009-trailer?browse=l
And pay attention to the following:
1. The Lighting.
2. The Overall Atmosphere.
3. The Car Explosion.
4. The Faces of the characters.
5. The Motion of the characters.
There's examples of both 3,4,5 passing the "Uncanny Valley" a little.
They could of made the car explostion uber realistic, but that would of required more resources and a lot faster system. This is the problem with making games "realistic" looking, the flaws stand out a lot more and a much more powerful system is needed.
On the other hand if you look at games like Braid, it's as far away from realism as you can get. Braid has a "dreamy" feel to it so it can get away with just about anything provided the world remains interesting. No need for high polygon models and heavy physics.