Hard Rain

Hard Rain is a new campaign for Left 4 Dead 2. Hard Rain takes place after Swamp Fever and is set in an industrial park that contains a sugar mill. At the start of the campaign, your ferry driver from the previous campaign drops you off, with the mission to return with gas for him. He tells you to signal him once you're done, but it appears that your group has forgotten the gun bag, which contained the flare guns necessary to signal the boat.

This campaign's Uncommon Common are the Worker Infected, that are immune to headshots and are not attracted to pipe bombs.

Trivia

 * This campaign contains a new gameplay mechanic called Hard Rain. Lightning flashes signal that a downpour is coming, which will summon a horde.
 * The background of this poster implies that the Survivors will have to go through an industrial zone of some sort.
 * In this campaign's poster Rochelle holds a scoped machine gun, most likely a MP5 Navy. This weapon is also in most Left 4 Dead posters, but is not in either Left 4 Dead or Left 4 Dead 2.
 * An area in this campaign known as the sugar mill, confirmed by the achievement Sob Story where one must navigate the sugar mill without killing any Witches, which seem to be attracted by the sugar scent.
 * Given that the campaign that follows this one chronologically, The Parish, starts out on a dock, it is reasonable to assume that the escape vehicle in this campaign could be the same boat as the last one.
 * The name could be a reference to the film Hard Rain, which involved a town dealing with a flood.
 * This is the first campaign in which the Survivor's loss of equipment during the introduction is explained.
 * Hard Rain is the second campaign (or first, chronologically speaking) to take place at daylight. It appears that it is morning in at least one chapter - though it can easily be mistaken for night when it begins to rain.
 * This is the only campaign to reuse the same levels, as they must go from the dock to the gas station, and then back to the dock. The only difference is the levels that are replayed are flooded by the rain from the first chapter, which eventually grows into a hurricane.
 * The Survivors seem to carry green gas cans on their back, most likely after the third level where they travelled to a gas station to get fuel for the rescue vehicle.
 * Part of this campaign seems to be in daylight, which will, of course, lead to Wandering Witches.
 * The weapons from Left 4 Dead will appear in this campaign.
 * There is waist-high water in the second half of the campaign, making it so that you walk at a considerably slower pace and makes it difficult to move around.
 * In an interview with Chet Faliszek, it was revealed that when traversing back to the boat, you will have multiple options on different routes to take (like roofs) to avoid water.
 * Also at the beginning of the campaign you start off with nothing but pistols or melee weapons unlike a normal campaign where you get weapons and a med-kit.
 * Hard Rain introduces a new Uncommon Infected, the Construction Infected. They are immune to Pipe Bombs and loud noises (due to earmuffs, and can take more damage and headshots due to their hard hats and uniform.

Links
http://www.youtube.com/watch?v=ey26-m_MVlw&feature=player_embedded - New weather effects are added, and the chainsaw can be seen from 1:57 - 2:45.