Zombies

The zombies are the main antagonists of No More Room In Hell. Those were once people, who succumbed to the virus 732-ZH and turned into the undead.

Shamblers
They are your slow zombies, they absorb a lot of damage unless it's directed at the head and can claw the player to harm them. In addition, they can grab a player (immobilizing them) and deliver bite attacks, which may cause infection and possible bleeding.

Runners
Unlike the Shamblers, runners can sprint towards players. Other than that their attack methods are exactly the same; in addition their health is lower so they can take less body shots before going down, and only one or two hits to the head are needed to kill them.

Children of the Dead
Also called as Children. Children are faster than Shamblers but aren't as fast as runners. They have a faster attack speed, but they're unable to grab and bite players. They are the weakest zombie type in NMRiH; a player can easily take out a child zombie with only a single bullet or a swing of a melee weapon.

Crawlers
These zombies are slower than the normal zombies you see. They do a great job of camouflaging themselves in the remains of the dead. They can still grab the player and infect them. Shoving does not do much. They can be killed with any weapon easily.

Burning Zombies
Rarely, if you set a Shambler on fire, they might 'morph' into a special kind of zombie where they're now able to sprint rather than walk, and may deal double damage. These zombies should be dealt with first since they have the element of surprise (an entire group of survivors can get wiped out). Eventually, the fire will scramble the brain and kill the zombie.

Survivor zombies
If a player is bitten by a zombie and dies after a couple of minutes due to infection they will die by falling to their knees then collapsing to the floor. After 3 seconds their model will change to their zombified self and get up from the ground. They will behave like a runner.

Controversies
Children of the Dead Controversy (from Kotaku) This was the controversy:

If you see a kid in a game, chances are it's one of the few things that is magically immortal—and the reason why is probably obvious. Child murder in games controversial...but that doesn't mean all developers consider it off-limits.

Granted, in this case, we're not just talking about any children—we're talking about zombie children. No More Room In Hell  is a co-op first person survival horror game where you fight against zombies. In an effort to make it tense, the developers made design choices like having sparse ammo, and only allowing players to communicate with one another if they are actually close in-game. Another curious design choice: one of the zombie types happens to be child zombies. Not everyone is happy about this. Looking through the threads found in the Steam community hub for the game, you'll find that a number of players are currently arguing over whether or not children zombies should be included.

In response to complaints and requests to remove the zombie children, a  No More Room in Hell project manager posted an announcement in the discussion forums, which can be found here:

MESSAGE TO THE NMRIH PLAYERS

Trivia

 * If a zombie bites you, there's a possibility that you'll get infected.
 * Children of the Dead are the fastest yet weakest zombies in NMRIH, but you should kill them fast, as they can deplete your health rather quickly