The way a game looks is the second most important factor while playing a game, but is always what grabs attention during a trailer or showcase. Not only does it have to stand out, but it usually has to be masterfully crafted to create total cohesion between itself, the gameplay, and the game's themes. As well, it can easily put somebody off of the best game to ever be made if the art does not feel as well painted as the game is designed.
For this exercise I choose to analyze Team Fortress Two.
Its painted textures and cartoony shaders make it a one-of-a-kind in fps games, which usually go for the ironically watered down realistic stylings. TF2 is so unique in it's graphics that it has lived on for almost 18 years, although the other factors the game has do a tremendous amount of work. But the art is not to be discredited, still. I have to admit that the visuals have gotten worse since release, but on release they were straight out of a comic. It was cel shaded, saturated to make everything contrast everything else, and even had physical shooting particles that weren't just the standard muzzle flash.