No Mercy

No Mercy is the first campaign in Left 4 Dead, spanning five chapters. 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 News 5 rescue helicopter: "To anyone who can hear this, proceed to Mercy Hospital for evacuation". Even if it means shooting your way through narrow alleys, open sewers and seething waves of Infected to get there.

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. But, in The Church, it took roughly an hour for the Church Guy to become infected after being bitten.

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.

Behind the Scenes
No Mercy looked significantly different in early versions; it was much darker, but where there was light, it would be quite bright. In addition, the skyscrapers and other buildings in the background would be a part of the skybox texture, which makes them look completely flat; in the final version, the buildings dotting the landscape are actual brushes and models. The sky itself was a dark blue, compared to the blue/green mix in the final version. Buildings in the campaign would have most of their lights still on, which was changed to very few of them in the final game.