Personally I don't have a strong preference between light or dark graphics. In general, variety is good, and extremes not so much (too light might not fit the subject matter, while too dark could make everything look the same).
I'm with Raze on this one.
I don't care if a game is 'Dark' or 'Light' or somewhere between as long as the game play is good and it doesn't look like an Anime.
Some of my favourite games look like actual cartoons (Broken Sword 1 & 2, for the curious) but the art style fits with the games.
Just give me an interesting plot, solid characterisation and good game play and I'm happy
