Half-Life 2

Valve scrapped the first Half-Life and restarted, playtesting from early on. Two months before it was due to ship, the first Half-Life could not be played start to finish, its levels did not tie together, and it had serious technical problems, so Valve scrapped it and started over. In the restart, playtesting began about three months in.

Testers were random gamers recruited from game shops and registration cards. The near-disaster became the origin of Valve's weekly playtest habit. Quote: "you couldn't play the game all the way through, none of the levels tied together well"

About 100 testers per chapter let Valve act on trends, not outliers. Each Half-Life 2 chapter was tested with about 100 players, enough to see common patterns and ignore a few odd results.

Watching hundreds of sessions also built design instincts, producing rules like 'players don't learn when stressed' and 'players don't look up'. Gabe Newell: "after you've watched a couple hundred playtests, you start to develop a much better sense of what are successful and unsuccessful design strategies"

The designers who built a level watch its playtests themselves. Valve does not hand testing to a separate department or publisher; the people responsible for a level or mechanic run its tests. In Half-Life: Alyx, designers saw players cover their real mouths to stop Alyx coughing near the blind zombie Jeff, and made it a mechanic.

Watching directly shows designers exactly what to fix, motivates them and sparks new ideas.

Watch where players struggle and add the missing aid. Half-Life testers broke every crate in a level, so Valve put ammo and health inside some of them.

Each test produces dozens of small changes like this. The same habit gave Left 4 Dead its x-ray outlines of teammates in trouble.

Testers loved the gravity gun, so it arrived much earlier. Half-Life 2's gravity gun was made available much sooner than planned because playtesters loved it.

Player response decided both what stayed and when it appeared; on Portal 2, a wall-walking paint was cut because it made several testers queasy.

Filter feedback through your goal: Valve kept the slower intro. Testers loved the short stretch before Gordon gets a weapon and wanted action sooner, but Valve still delayed combat so players would first witness the Combine's cruelty and the crowbar payoff would land harder.

Bending to every tester leads to design-by-committee sludge; go in with a specific game and audience and test whether you hit it. Writer Marc Laidlaw: "We wanted you to witness the cops doing something horrible, and feel like what you were doing was a response to that"

A new medium needs retesting: VR players tolerated less talking. Testing Half-Life: Alyx showed players' patience for standing and watching characters talk was much lower in VR, so Valve sped up the pace.

Valve's Christine Phelan: "You could almost think of the player as another designer."

Steam data exposed a difficulty spike, which Valve patched. Post-launch data showed many players stuck in Half-Life 2: Episode One, so Valve patched a tricky siege battle to make it easier.

Online play turns millions of players into ongoing playtesters.

Props teach mechanics and dangers without tutorial popups. A saw blade stuck in a sliced zombie hints that saws work with the Gravity Gun, and an enemy fried on a fence warns you not to touch it.

Quote: "A saw blade stuck in a sliced-up zombie suggests using these saws with your Gravity Gun to defeat enemies."

The Citadel looms on the skyline as a goal to move toward. Like Disneyland's central castle, the Citadel gives players a distant landmark to work toward and a fixed point to navigate by.

Quote: "give you something to work towards and a static position to aid navigation"

Level architecture builds oppression to match the story. Narrow corridors, tall buildings, cages and cameras make City 17 feel claustrophobic and watched.

The overpowered gravity gun upgrade is held until the end. Half-Life 2 only upgrades the gravity gun late, because such a strong ability would make it hard to build challenges that constrain the player.

Mind Over Magnet used this as its model for saving its powerful instant recall for the end. Quote: "it's really hard to make walls that can hold the player in."

A loud flatline sound confirms a Combine soldier is dead. Combine soldiers play a distinctive flatlining sound when they die, so players, including those with low vision, know the kill landed.

Quote: "It's also important for a game to have a really vivid soundscape"

Full closed captions cover gunshots and explosions, not just speech. Half-Life 2, like most Valve games, captions gunshots, enemy chatter and explosions, letting deaf and hard of hearing players follow events even outside their view.

The weakness is that the captions do not say where a sound comes from.