No Mercy

No Mercy is the first campaign in Left 4 Dead, spanning five chapters. It is also, chronologically, the first campaign in Left 4 Dead 2, as it was officially ported into Left 4 Dead 2 in The Sacrifice DLC pack. The first level picks up right where the game's introduction cutscene leaves off; the Survivors are told by a passing helicopter to get to Mercy Hospital to be evacuated. On their trek to the hospital they must endure Infected-filled apartment buildings, city streets, subway tunnels, and sewers, passing through Mercy Hospital until they finally reach the roof of the hospital itself to be rescued by a helicopter.

Below is a complete list of video walkthroughs of the 5 levels:

The Sewer Part 2
 * 1) The Apartments
 * 2) The Subway
 * 3) The Sewer Part 1
 * 1) The Hospital
 * 2) Rooftop Finale

Please know that the gameplay videos are on each campaign's info page not on each map page.

Official description
The No Mercy campaign finds you on the rooftop of an obliterated apartment complex, deep in the heart of the once-thriving metropolis of Fairfield—now completely overrun with hordes of Infected. A voice from a bullhorn calls out from a rescue helicopter: Get to the roof of nearby Mercy Hospital and be airlifted to safety. Even if it means shooting your way through narrow alleys, open sewers and seething waves of zombies to get there.

Left 4 Dead 2
With the Sacrifice and Cold Stream DLCs, No Mercy was edited and ported over to Left 4 Dead 2. Thus it included all the new infected, items and weapons giving a whole new experience. Video walkthroughs made by youtuber Rusty Woud show off the Left 4 Dead 2 version of the campaign and all the changes:
 * 1) Maps 1 and 2
 * 2) Map 3
 * 3) Maps 4 and 5

Graffiti
The Apartments level contains graffiti throughout the map. Much of it is located in the safe room across the street, but some is found on the level start area. "Hope" is spray painted in large letters to the left of the doorway, with "NO" written above it to change it to say "No Hope", and "Morbid" can be seen on the right wall, also in graffiti-style lettering. These can show the panic and almost instant surrender of the people who saw the Green Flu take hold.

In the safe room, "None of you will survive" and "Entire city is Infected, if you can read this, get out", are among other things written by other survivors. In the finale, there is a written conversation on the wall talking about the duration of the change to Infected after being bitten from 5 days, 3 days, 1 day, 2 1/2 hours, then finally, to 5 minutes.

Demo
The Left 4 Dead demo consisted of The Apartments in its entirety, as well as most of The Subway. The rest of the Subway map could be seen in the demo if players went into Noclip mode.

Achievements

 * See Main Article: Achievements

The following Achievements are only available in after No Mercy is complete.

Behind the Scenes
No Mercy's lightling effects underwent marked changes during development. Early on, the contrast between light and shade was accentuated. Ambient light in each scene was suppressed making for a dark and ill-lit enviroment and where there was a light, it was made extremely bright.

Skyscrapers and other buildings in the background appeared unnaturally flat because they were a part of the skybox texture. Since this does not affect gameplay, this may have been done deliberately to speed up the game's development for play testing purposes. In the final version buildings are rendered as actual brushes and models.

The sky was once a dark blue as compared to the blue/green mix in the final version.

Buildings had most of their lights on. In the final version only scattered windows are illuminated.