Lowlife

Introduction

The Stalker train car crashes at the end of Direct Intervention, forcing Gordon Freeman and Alyx Vance to continue on foot.

Maps

ep1_c17_00 - entering and traversing the underground tunnels.
ep1_c17_00a - multi-storey parking lot at the start, flooded section in the middle, big Zombie arena with the lift to the surface at the end.

Architecture

This chapter takes place underground, in abandoned car tunnels, collapsed parking lots, flooded basements.

With the Citadel left behind, this chapter mostly sees the use of concrete floors and walls, damaged ceramic tiles, dusty and grimy overlays.

Environment

Lowlife creates a hostile, lonely, abandoned environment. The protagonists don't meet anyone else - everyone has either left, gotten killed, or turned into a Zombie.

The deterioration of the city infrastructure, brought on by the many days of street wars and the Citadel being compromised, is very evident.

A lot of regular human trash litters the passages. Blood and gore is not uncommon, as the rebellion has been going on for over a week in Half-Life 2. Most tunnels lack sufficient lighting, the space is filled with debris and car wrecks, barnacles were allowed to spread freely.

Glowing exit signs on emergency power are appropriate. The lighting is usually sharp and cold, coming from fluorescent lights, or reddish, dim and uneven, coming from fires. Safe areas and map transitions are usually lit with warmer and steadier lighting from undamaged caged lamps.

As Alyx points out, the city perimeter is no longer secure, letting Antlions infiltrate the place. Their burrows are encountered in the parking lot on ep1_c17_00a. This occasionally informs the choice of terrain, as the burrows should be placed on something soft enough for the Antlions to dig through (sand, dirt, gravel, pulverized asphalt).

Lack of lighting makes emergency flares come in handy. They produce dynamic lighting in a short radius, and can set Zombies ablaze, which in turns gives more light.

A new gameplay element is the Power Boxes. They essentially work as slightly fancier switches with a model tailored for these purposes. They are placed as npc_furniture and work in conjunction with a scripted_sequence; however, similar result can be achieved with a mere prop_dynamic having SetAnimation inputs fired at it.

Occasionally, Combine tech can still be encountered - depleted Sentry Turrets, Combine Lights, inactive forcefields, crashed Combine Trains.

NPC's

Numerous Classic Zombies, Fast Zombies, a few Poison Zombies. The game introduces the Zombine here.

Headcrabs of all types.

Antlions spawn constantly out of their burrows, unless plugged up (covered by a large prop). To disallow the player from leaving without dealing with it, areas with these burrows typically feature a Momentary Door kind of lock at the exit.

Barnacles are featured frequently, as enclosed spaces and darkness make for the perfect setup for them.

Hoppers are about the only Combine security measure still performing adequately in this chapter.

Naturally, zombies and the bugs infight, and Barnacles pick up either indiscriminately.

Trivia

Originally, the Power Boxes were designed with Alyx in mind. The player would have to cover her as she was "hacking" the box. However, this proved to be unconvincing and frustrating,[1] so the player can readily operate any Power Boxes they encounter. The animation for activating a Power Box is still called hackPowerBox as a remainder of that, and Alyx still possesses the related animations.

Another idea that didn't make the cut was Alyx's ability to dispense emergency flares.

Lowlife showcases a new NPC feature - dynamic interactions. This gives Alyx the ability to engage enemies in close combat, evading their attacks and finishing them off.

Yet another new feature at play here is the darkness system. It affects companion speech for Alyx, her ability to detect enemies, the player's flashlight illuminating enemies, Alyx's reaction to shining the flashlight in her face, burning entities providing limited light for AI purposes.

Lowlife is also the first time where Zombies enter their 'slump' mode as part of an actbusy system rather than scripted sequences, as was the case in Half-Life 2. This also means they can actually go back to sleep at one of the actbusy hint nodes, if they were woken up but didn't detect the player for some reason.

Reference

An example of gloomy lighting in Lowlife.
Ditto.
A car tunnel featuring Zombies, Hoppers and Sentry Guns. Note that the latter are out of bullets (using Out of Ammo spawnflag).
A Zombine in a crashed Combine Train.
A flooded basement.
A glowing exit sign, behind it a warmer light illuminates the staircase.
An Antlion burrowing out in an underground parking lot.
A bigger parking lot with more burrows.
A crank (momentary_rot_button) preventing the player from exiting the area quickly.
The final goal of the chapter - the lift to the surface. At first it is illuminated by the lamp. Later, with lights off, the arriving lift itself will stand out in the darkness.