I have just completed Crysis 2 on my Xbox360 and what I can tell you right now is Crysis 2 on Xbox360 is easily one of the best looking games of this generation. But now, everyone wants to know how the game stack up against Sony's exclusive FPS Killzone 3 in term of visuals.  
First of all, you have to consider one thing when you compare Killzone 3 and Crysis 2 graphically: Killzone 3 is designed like a corridor shooter while Crysis 2 isn't. Yes, sometimes you will travel through a linear path with cinematic moments, story and dialog in Crysis 2, but when the actual gameplay begins, you will be roaming in wide areas with multiple paths. On the other hand, Killzone 3 stages give the player the illusion of being in large areas, but the fact is: Killzone 3 is linear and feel much narrower compared to Crysis 2. So you have to consider the scale of the stages in each game and the fact that Crysis 2 is rendering more stuff on screen than Killzone 3.  
 
 
 
When you create open areas with state of the art visuals on consoles there is always a cost. Crysis 2 suffer from texture pop in/out and some unstable frame rates. Killzone 3 feel smother and doesn't suffer from texture pop in/out issues.  
One area where Crysis 2 shines over Killzone 3 is in the impressive lighting technology of the Cryengine 3. Crysis 2 lighting effects are the best I have ever seen in a videogame. On top of that, Crysis 2 render more light sources than any game on the market right now. Crysis 2 is leagues beyond everything else out there. I have never seen an engine handle the sheer magnitude of light sources with the ease that Crysis 2 does. Light is coming from everywhere and casting shadows on everything. Search lights from choppers, yellow flames belching from car engines, and explosions from a rocket launch all add their light to the scene. The battlefield becomes chaotic with objects, combatants, and light sources dancing across the screen. Even the aliens eyes cast dynamic lighting. Also, CryEngine 3 is the first real-time graphics engine to implement a global illumination model which means that it simulates light bounce and even uses light propagation volumes to introduce color bounce and indirect lighting.  
Each game has a different anti-aliasing method to get rid of the jaggies. Killzone 3 is using a solution called MLAA while Crysis 2 is implementing temporal AA. Crytek have said that their solution will give better result than Sony's MLAA solution. What I can say right now is Crytek solution is variable. Also, Crysis 2 has bigger and more open environments, which means that Crytek's solution has more edges to smooth out. Also, the darker and less colorful art style of Killzone 3 make the jaggies look less noticeable. In Crysis 2 during the high contrast or bright levels, the jaggies look more noticeable than in Killzone 3. But in darker levels like the ones in Killzone 3, the solution work much better and it would be hard to anyone to notice any jaggies. Which means that sometimes Crytek solution give us the same great results of MLAA and sometimes it doesn't.  
 
 
 
While arguing in which game has better artistic design is debatable, I found the art style of Crysis 2 to be more appealing. Crysis 2 artistic design is more colorful, organic and varied than Killzone 3. When you about to get bored off the great looking foliage, water and buildings in Crysis 2, the game takes you to completely new type of environment.  
To be fair, both games offer some of the best visuals of this generation. Each game look better than the other in various places. But for me, I found myself more amazed by Crysis 2 visuals due to the state of the art visuals, great art style, and varied environments. Also, the campaign mode in Crysis 2 is more fun, much longer, and more repayable than Killzone 3 story mode.  
Take a look below at some screenshots (off screen) I took while playing Crysis 2 on my Xbox360:  
 
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