Grenade Indicator
When a grenade lands nearby whether it's a friendly or enemy grenade , a grenade icon appears in the center of the screen. In addition, a small arrow near the icon points toward the grenade's location. If you are standing directly over the grenade, the icon changes to a hand holding a grenade. Once you see this icon, you can hit the Grenade button to pick up the grenade and toss it back at the enemy.
look inversion
During the tutorial level, make sure to look up and down a lot. If you have any difficulty figuring out which way is up and which way is down, it likely means you prefer to play with look Inversion enabled. You can adjust this during the tutorial or at any other time by adjusting the option under the Controls submenu on the Pause screen. Take a couple of shots and the screen turns light red. Sustain a couple more hits and the screen becomes very bright red on the edges and the on-screen view...
aim assist
Aim Assist is a special feature for the Xbox 360 and PS3 that enables you to more accurately fire at enemies in the single-player campaign. When this feature is turned on, your sight automatically snaps to a nearby enemy when you press the Aim Down Sight button. Aim Assist activates only when the player quickly pops out and back into Aim Down Sight mode.