Copy and pasted from here: http://foxyurl.com/MB5 (detailed info)
- 5 new campaigns, including Dead Center, Dark Carnival, Swamp Fever, Hard Rain, and The Parish.
- New game mode: Scavenge! All game modes will be available at launch.
- 4 new Survivors: Coach, Rochelle, Ellis, and Nick.
- At least 20 new weapons and items.
- New melee weapons: axe, chainsaw, frying pan, baseball bat, cricket bat, katana, guitar, crowbar, machete, and tonfa.
- New ranged weapons. Ranged weapons at least include new pistols (including a magnum), SMG, new pump and auto shotgun, grenade launcher, and at least a few new rifles.
- Some old weapons from Left 4 Dead 1 may be included in the new game.
- More powerful AI Director 2.0.
- New Infected types, including at least 3 new SI (e.g. Charger).
- Some daylight gameplay. At least one campaign occurs at night.
Wikipedia
In
Left 4 Dead 2, the Director has been improved to encourage more participation by players, forcing players through difficult gauntlets to reach the extraction point. It also has the ability to alter elements of the level such as placement of walls, level layout, lighting, and weather conditions, making each play session unique.
http://en.wikipedia.org/wiki/Left4Dead_2#cite_note-rps_preview-3 The Director now rewards players for taking longer or more difficult paths through each episode by providing more useful equipment, such as incendiary ammo, along these riskier paths.
http://en.wikipedia.org/wiki/Left4Dead_2#cite_note-e3preview-2
A new addition to
Left 4 Dead 2 are the "uncommon infected" unique to each campaign. By virtue of equipment worn before infection or mutation, they possess an ability that separates them from the common infected. For example, in the Parish campaign the player encounters infected wearing
riot gear, making them almost impervious to gunfire from the front, while Dead Center features infected with
Hazmat suits immune to fire.
Several new Special Infected are introduced in
Left 4 Dead 2, all of which are playable in versus and the new Scavenge game mode.
http://en.wikipedia.org/wiki/Left4Dead_2#cite_note-rps_preview-3http://en.wikipedia.org/wiki/Left4Dead_2#cite_note-OXM_50_Specials-18 The Charger is an infected with a mutated, oversized arm, able to move quickly and knock players in its path off their feet. It can also grab players and smash them against the ground to deal major damage. The Spitter can project balls of mutated, acidic phlegm that splatter across an area, eroding the survivors' health as long as they remain within it. The Jockey can jump onto the back of a survivor and steer them into other infected or terrain traps set by the Director.