Killing enemies and completing objectives earns you XP. (Some people claim that you can earn xp using system link or split screen, but Cod6 Modern Warfare 2 doesn't share xp between online and local play). XP boosts your level and lets you unlock new guns, new equipment and new skill boosting bonuses.
New weapons expand your potential arsenal, but the new equipment actually adds some new tactical wrinkles. The blast shield will help you survive against trigger happy opponents and the tactical insertion flare lets you mark your next respond point which can be a real game changer in objective based modes like demolition and domination.
Perks, which are handy battlefield skills and enhancements can be upgraded through use and will eventually grant you another bonus.
New death streak perks kick in when you've died a few times in a row. Some are familiar, like the infamous "drop a grenade when you die" martyrdom, while others offer aid to new players in early stages, like copy cat, which allows you to mimic the class of the person that killed you. This allows lower ranked players to copy the weapons and perks of the person that killed them and nothing helps to ease the frustration of being holed by a gun you haven't unlocked yet, by getting to use that gun yourself.
Elements from the campaign also play a part in multi player, like the bullet resistant shield. Equip this aa your primary weapon and bullets will bounce right off it, allowing you to infiltrate heavily defended positions.
Team two shield protected players together and you have a whole new entity to deal with.
Another carry over element is the excellent predator drone missile, which is one of the many customisable kill streak rewards.
The result of these many multi player tweeks is a substantially busier battlefield. yet despite all that's going on, the action usually peaks at intense and doesn't boil over and become overwhelming.
Although the core AI remains familiar, competitive multi player in CoD6 Modern Warfare 2 is the best in the series and is sure to be a must have for shooter fanatics.