The original Call of Duty was widely praised, but it still got some negative feedback on certain ideas. So Infinity Ward has added some new features in the second installment to enhance gameplay and help the player.
The health bar seen in the previous games is now replaced by a "shock system". If you get hit repeatedly (the exact number of hits depends on the difficulty level), your screen will turn red and you will hear your character's heavy panting and heartbeat. This eliminates the health packs used in the previous games and adds a very slight touch of realism.
In the past, your only way of detecting grenades was listening to them clink right next to you. Now, an arrow points to the location of the grenade, allowing you to run in the opposite direction. Additionally, grenades do not count as a weapon slot any more; a special button may be pressed to throw grenades. They can't be cooked any more. Colored smoke grenades are also added.
Scoped weapons now have much more movement than they did before. To steady them, you must hold your breath, usekey to do this. Additionally, the crosshair turns red when pointed at an enemy. Several weapons have been added, removed, and replaced as well.
You can now jump over small obstacles. You can't jump very high, but it helps when trying to get round sandbags and walls. When near a wall an indicator will usually allow you to jump over it. Jumping should not be used to try and dodge bullets.