Pretty graphics are always a plus in a video game. Even though MW2 is running on the first Modern Warfare game engine, Infinity Ward has done fantastic job improving it. The game features a new hi-res Texture Streaming functionality that allows much larger environments, with more detailed characters and landscape.
You can enlarge the image below for a better view.
As you can see, there is a huge difference in the character model, especially in the hair. The game is no Crysis, obviously, but the visuals are appealing and well done, PC users can look forward to maxing the game out.