Left 4 Dead 2

Like its predecessor, Left 4 Dead 2 is a first-person shooter with a heavy emphasis on cooperative gameplay. The game presents five new campaigns, each composed of three to five smaller levels. As in the first game, each campaign is presented in menus and loading screens as a film starring the four Survivors; and features, upon completing a campaign, a faux credits screen which acts as the final scoreboard for the players and recaps certain performance statistics for the group. In every campaign, most levels involve the Survivors attempting to reach a safe room and close the door once they are all safely inside. However, the final level in each campaign requires the Survivors to call for rescue and either survive a prolonged onslaught until rescue arrives, pass through an especially challenging gauntlet of Infected to reach an escape vehicle, or collect and utilize fuel cans to enable their escape.

Each Survivor can carry one each of five categories of equipment: primary weapons, secondary weapons, throwable weapons, major medical supplies (which also includes ammunition upgrades) and minor medical supplies. Primary weapons are broken down into four tiers based on their availability and attributes. Tier one weapons (such as the SMG and Chrome Shotgun) deal damage relatively slowly and serve as basic offensive weapons. Tier two weapons (such as the Assault Rifle and Combat Shotgun) deal damage faster and often appear in later maps of each chapter.

Like its predecessor, Left 4 Dead 2 is set in the aftermath of an outbreak on the East Coast of the United States of a disease nicknamed the "Green Flu", which rapidly transforms humans into zombie-like creatures and mutated forms that demonstrate extreme aggression towards non-Infected beings. A few humans are immune to the disease, while some of those who are Infected have no symptoms. S. military create safe zones to attempt to evacuate as many survivors as possible.

Left 4 Dead 2 introduces four new survivors: Coach, Ellis, Nick, and Rochelle, who are immune to the disease and have individual backstories that are provided through character dialogue. While the game is intended as a continuation of the original, occurring one week after the first game begins, Valve decided to create a new group of survivors due to the change in location. Like the first game, the five campaigns in Left 4 Dead 2 take place across a story arc. Set in the Deep South, the story begins in Savannah, Georgia, and ends in New Orleans, Louisiana.

Development for Left 4 Dead 2 started shortly after the release of the first game—following a short break—building on ideas from the development team to make the next game "bigger and better". According to Chet Faliszek in a 2023 interview, Left 4 Dead had been developed quickly to release as soon as possible that it left the game in a bad state that no one at Valve wanted to work on correcting the issues to improve the game. Instead of trying to fix features and include new features like mod support, the team opted to completely rebuild the game as a new title, properly addressing strong development steps to avoid the miscues from creating the first game. The game was given the code name "Carnation" by Microsoft to prevent revealing its details before its official announcement.

Faliszek stated that Left 4 Dead 2's story would explore more of the world of the game, and that Valve had created a full story for the cause and effects of the infection pandemic, including terms that they have used for the AI Director. Each campaign was purposely designed with a different feel; however, all five campaigns were mapped out at the same time by the entire team to provide the narrative flow and ensure the uniqueness of each campaign. The team used a Left 4 Dead dictionary developed to describe level design and flow within the game to provide a common language for developing the levels.

Left 4 Dead 2 received "generally favorable reviews" across both platforms according to review aggregator website Metacritic. Game journalists praised the changes made with the new melee weapons and firearms, the new strategies introduced through the new special Infected, and the details of the southern locale and individual campaigns compared with the campaigns of the first game. Ars Technica praised the game's replayability and the attention put in every detail. Libération also praised the game, commenting that Valve was one of the last game studios making games geared toward hardcore PC gamers.

IGN considered that the game improved on the first in every way, and that anyone who liked the concepts introduced by the first game should buy the second. Eurogamer also praised the game, and considered that it was "overflowing with personality". Left 4 Dead 2 received the Best Xbox 360 Game award at the 2009 Spike Video Game Awards. E.