The official Crysis 2 website has put up some info on what game modes the maps have and a one line sentence on the 2 new weapons.

Game Modes available on specific maps:

• 5th Avenue – Instant Action, Team Instant Action, Capture the Relay, Crash Site.
• Chasm – Instant Action, Team Instant Action, Crash Site.
• Plaza – Instant Action, Team Instant Action, Assault, Crash Site, Extraction, Capture the Relay.
• Prism – Instant Action, Team Instant Action, Capture the Relay, Crash Site.
• Apartments – Instant Action, Team Instant Action, Crash Site, Assault, Extraction.

Weapon:

• FY71 – Assault rifle effective up to medium range, with high damage and low rate of fire.
• Smoke Grenade – Used like a flashbang but on detonation deploys a large volume of smoke, blocking vision.

The Decimation Pack is now available for download on Xbox 360, The price is 800 Microsoft Points (Xbox 360).

Source: Crysis 2 official website