One really cool thing is that the opposition hides behind cover and reaches their weapon over it to fire at you having a really small footprint for you to shoot at. Adds to the level of realism, I think. Another nice feature is that when you hide behind cover, you can peek as little or as much as you want, and because it is mouse-controlled, it is very precise. I managed to save myself several times by the quick mouse response to get back to cover after peeking over something.
That cover mechanism is something I first saw in Rainbow Six Vegas... excellent idea. In R6V, you click and hold RMB close to a wall or any cover and your character hides. You then get a 3rd person view of yourself whereas the crosshair is free and you can aim and shoot, both blind (just pop your gun above your head and spray and pray) or poke your head out and land a precise headshot ;D ;D ;D
Don't know if it was the first game to develop such mechanism, but it was a hell of an improvement in shooters alike... GTA IV uses it too and now COJ2.
Bullet time and cover system makes for a great action game 8)
The cool thing that Ricamundo would appreciate is that you remain in first person when you peek, and all you need do is approach something and move the mouse in the "Y" axis to take cover/peek. Really works kind of slick.
Good cover mechanisms are all the rage now. Killzone2 had a great cover method that also left you in first person. What realism when your huddled close to concrete rubble or the side of a tank with excellent details and bullets are whizzing overhead busting up the concrete or whatever. That's cool that COJ has first person cover.
ArmA2 has peek around a corner, which you can use as a toggle (press= peek, release = turn back to cover) or double-tap the key and your head remains in that peek (relaxing for your keyboard hand, haha). Double-tap again to switch back to toggle mode and turn back to cover. All can be done either 1st or 3rd, your choice.