Alex it's a Mod for Half-Life 2
It's called
"No More Room in Hell" and it's basically a Hardcore Left 4 Dead. With (mostly) slow zombies that you need to hit in the head to effectively kill.
Multiplayer only, there's two modes:
- Objective: like in L4D, you go through the Map, do different tasks to eventually call in an escape method, have a last stand and try to escape
Dynamic maps, each map has multiple branching points and at the start of the level those are randomly determined (mostly branching - one game a door is open / the other time it's locked and you need to go through a fence instead; one game you need to find fuel to start up a generator in another game you need to find a blow torch to cut your way through a steel door etc.)
Ammo is scarce, you can't kill everything and have to navigate through hordes of zombies without engaging / just shoving them out of the way quite often
One life only (or on very long maps maximum one respawn option roughly halfway through the the map). Time to get through a map: highly dependent on the map and group but it can take between 10 to 20 minutes I guess.
Friendly Fire enabled by default.
Melee system where Zombies can grab you (you can also shove them away / out of the way).
Weight system where you can't (and also shouldn't) hoard everything.
Teamplay needed to survive - no Rambo shit here.
Contracting infection from Zombie bites is possibly (chance depending on how low your health is), after being infected you need to find medicine for it or you'll turn.
Running and Melee attacking costs Stamina, once you're out it takes some time to catch your breath again. Further discouraging running & gunning your way through the hordes.
- Survival: 10 waves of zombies attack a certain location, you just need to hold your ground and kill 'em all
More Guns/Ammo than in Objective mode
If you die, you'll respawn at the start of each new wave
Barricade system with wooden boards and boxes
Some maps need you to hold more than one location
Negative points:
Many people seem to lack the patience waiting for a respawn when they die (damn noobs), encourages "Server hopping"
While there's a nice variety in Weapons both Melee and Ranged, there's a distinct lack in different Zombie types. You got Slow ones (majority), Kids (faster, harder to hit), Runners (faster), Risen Survivors (Spawn from dead, infected players - fast and can take more bullets I think)
Oh and as you saw in the Screenshots there's dismemberment and also lots of gore (not shown in Screen but there's lots and lots of blood).