I liked the black and white desaturization. It certainly beats everything being shades of brown like in a lot of ther games. And I like stuff that is black and white because it's not done much in other games or media. Loved The Saboteur and there was a lot of b/w in that game.
Nothing wrong with it in Saboteur or in-general, it was just badly used in Conviction.
Saboteur it was cool because of how it emphasized color, was used as a (blunt) metaphor for restoring Freedom to areas, and really added to the aesthetic of the game.
In Conviction it serves no purpose other than to indicate you are in the dark. Even worse, since you are often in areas that are very dark, having the game go black and white makes it harder to see the environment.
If they HAVE to do it again at least just make Sam turn black and white or something less intrusive on the gameplay. Or just use the little light on Sam's gear to indicate it; it's easy to see, it's integrated into the gameworld, and it doesn't get in the way.