Modern Warfare 3 gets redesigned killstreaks, game modes, everything

Assault Strike Package – Pointstreaks within this package chain and are designed for more direct damage (Predator, helicopter, etc), just like in Call of Duty: Modern Warfare 2. Your streak resets on death.
Support Strike Package – Pointstreaks within this package do not chain. However, streaks do not reset on death. Streaks are more support oriented (UAV, Counter UAV, SAM turret, etc)
Specialist Strike Package – Pointstreaks designed for the expert players. Rewards come in the form of additional perks. A player activates additional Perks as they progress in a Pointsreak. These perks last until death.

Strike Packages include (not limited to):

Assault:
Streak count resets on death
5 kills: I.M.S.
9 kills: Strafe Run
9 kills: AH-6 Overwatch
10 kills: Assault Drone
15 kills: Juggernaut

Support:
Streak count does not reset on death
5 kills: Ballistic Vest
5 kills: Airdrop Trap
10 kills: Recon Drone
14 kills: Stealth Bomber
18 kills: Juggernaut Recon

Specialist:
Unlock one additional Perk at 2, 4, and 6 kill intervals for up to 3 additional Perks beyond the 3 Perks each player already has assigned to their custom load out at the beginning of a match

Death Streaks make their return in Modern Warfare 3 and include (but not limited to):

4 – Juiced (run faster)
5 – Revenge (last person to kill you is visible on radar)
5 – Hollow Points (increased bullet damage for 1 kill)
6 – Dead Man’s Hand (player falls into last stand with C4)

NEW WEAPON PROGRESSIVE RANKING SYSTEM: MW3 evolves your gun progression
Modern Warfare 3 features more than 40 of the most high-speed weapons that are either in-use or being field-tested by special forces:
Primary: Assault: SMG, LMG, Sniper Rifles, Shotguns and Riot Shield
Secondary: Machine Pistols, Handguns and Launchers
New weapon progression is designed to improve specific weapon leveling unlocks (attachments, reticules, and camos) and Weapon Proficiencies
Weapon Proficiency allows players to specialize their weapons with new attributes (some unique to weapon classes)

Proficiencies (not a comprehensive list):
Kick – Reduced recoil when firing
Attachments – Two attachments on Primary weapon
Focus – Reduced flinch when hit
Stability – Reduced sway when ADS

Attachments (not a comprehensive list):
Red Dot Sight
Silencer
Holographic sight
Dual Scope (Close Range/Long Range Optics)

NEW PERKS
Recon – Explosive damage paints the target on the mini map
Blind Eye – Undetectable by air support/sentries
Assassin – Undetectable by UAV, portable radar, thermal, heartbeat
Quickdraw – Faster aiming
Stalker – Move faster while aiming
Marksman – Identify targets at longer range

NEW GAME MODES
Fan favorite game modes make their return (Free-for-All, Team Death, Match, Domination, etc.), and a series of new modes make their introduction to the Modern Warfare series:
Kill Confirmed – Collect dog tags from killed players. Prevent the other team from collecting yours
Team Defender – Grab the flag and protect the flag carrier to increase your team’s score

NEW GAME MODES FOR PRIVATE MATCH
Infection – The infected kills enemies to recruit them for the infected team.
Drop Zone – Hold the Drop Zone for Team Points and Care Packages.
Team Juggernaut – With the support of a juggernaut, kill players on the opposing team. The first team to reach the score limit wins.
Juggernaut – Kill the Juggernaut to become the new Juggernaut
Gun Game – Be the first to dominate with every gun
One in the Chamber – Gain ammo by eliminating enemies. Be the last to survive.

CUSTOMIZABLE GAME MODES FOR PRIVATE MATCH
Private matches have been significantly enhanced to allow players to create new, customizable game modes in addition to the new modes for private matches (listed above) and share newly created games modes with friends.
Through ELITE, subscribers can vote on favourite new modes and those modes could make their way into public playlists.

MULTIPLAYER MAPS: 16 Maps – including the maps shown at Call of Duty XP:
Resistance
Dome
Underground
Village
Arkaden

DEDICATED SERVERS:
Modern Warfare 3 will support dedicated servers on Day 1. Players will be able to: browse, filter, favorite, and join Call of Duty: MW3 dedicated servers of their choice
Players will be able to setup their own server and administer their MW3 dedicated servers with direct control over features such as game rules, setup and ban lists.

SPECIAL OPS (CO-OPERATIVE GAMEPLAY):
Having made its introduction in Call of Duty: Modern Warfare 2, Special Ops makes its return in Modern Warfare 3 with a bevy of additions that innovate as a stand-alone mode, but also serves as an effective springboard into multiplayer action.