FPS's rely a lot on their graphics to increase immersion. They usually don't focus on story development as much, especially games like Call of Duty or Medal of Honor. In this capacity, it's perfectly legitimate to criticize them based on their graphics. As we all know, many of these games live or die based on their multiplayer, and graphics will play a huge pat in making you eel like you're really in Afghanistan or Russia or whatever gunning down terrorists or any other sort of enemy they've created for the game. In this sense, saying you didn't like Black Ops because the graphics weren't very good is perfectly understandable.
While on the flipside, a game like minecraft doesn't need to have amazingly detailed graphics. Not only because the game is pretty huge so it would be hard to support them, but because the game immerses you in different ways. Or take tetris. No one played or plays tetris for the graphics. These are simply some examples of games that don't need graphics to immerse you in what you're doing.
Just think about an answer to this question: If MW2 was streamlined to the point that it was inarguably the best FPS ever designed, yet it had the graphics of minecraft, would it be illegitimate to criticize it's graphics in a review?
Another quick question: If Star Wars had the special effects of Plan 9 from Outer Space, would it still be remembered as a classic film?
