While gearing back up for some more interactive fiction development after my two-and-a-half-month detour through Dragon Age, I made a comment on rec.arts.int-fiction to the effect that the Drama Manager in Blue Lacuna, Aaron Reed’s XYZZY Award-winning interactive fiction title, was unique in my knowledge in terms of providing an auto-adapting pacing mechanism for gameplay.

Zarf (Andrew Plotkin) responded with a link to a design postmortem presentation for the game “Left 4 Dead“, by Valve Software, which talked about their use of procedurally-generated content to provide dramatic pacing for that game.  Now, Left 4 Dead is substantially different from an interactive fiction title, but I like a good FPS as much as the next guy, and was intrigued by the paper.  In a coincidence that was happy for my wallet but not for my productivity, Valve was having a half-price sale for Left 4 Dead 2 right after this exchange, so I was able to pick up the game for just $25 and give it a spin.

The premise of the L4D series is that there’s been some sort of contagious infection that is turning people into zombies.  You play one of the four Survivors, humans that have proven immune to the contagion.  The goal is simple — escape the zombie hordes before your brains are eaten.  To do this, you have to work together to protect each other and carve a path through the ravening hordes of zombies to reach an extraction point at the end of the level.

It’s a cooperative first-person shooter game — even if you play alone, the game spawns three “bot” players to help you.  And it’s a good thing it does, because the gameplay depends on close cooperation between players.  If one person gets separated from the group, it’s very likely they’re going to get killed before too long, because certain of the enemies — the “special Infected” — can pin or otherwise incapacitate lone Survivors.  If one of your friends doesn’t quickly kill whatever’s on you, you’ll watch helplessly as the zombie rips you apart.

A big chunk of the magic of this game, as the paper I read indicated, is in the pacing.  L4D2 generates loot and enemies procedurally, depending on where you are and what your calculated level of “emotional intensity” is.  If you’ve been fighting hard, with lots of zombies on you, the game will hold at that level of intensity for a little bit and then back off to give you a breather.  If you’ve had some downtime, the game will slowly start spinning up more enemies and eventually subject you to a “horde”, where a mob of common Infected rush you, trying to overwhelm you with a human wave attack.  And every so often you get a special Infected or boss Infected thrown into the mix.

These special Infected are by far the toughest part of the game.  Each of the specials has a powerful ability it can use to wreak havoc on a team of Survivors.  Spitters can spit globs of caustic saliva, causing damage and potentially cutting off escape routes.  Chargers can sprint into a group, grab someone, and carry them along in a straight line until they reach a wall, both damaging and separating them from the group.  Jockeys can jump on your shoulders and force you to run away from your friends, and can even force you off ledges.  The dreaded Tank can absorb a ridiculous amount of firepower, and does amazing damage and knockback if you are foolish enough to let it close to melee range.

The complement to the dynamic pacing is the atmosphere.  Level design is excellent, with decaying architecture, weather effects, low-light areas, and close quarters all serving to keep the tension heightened.  The music used on each level is different, and thematically matched to the play environments.  Hordes and bosses all have special theme music, which is again different depending on the level you’re playing, and it wasn’t uncommon for me to start getting twitchy and panicky when I heard that horde theme start up again while I was stuck hip-deep in swampwater.

Your fellow survivors have a great deal of scripted conversation that is triggered in certain circumstances; you definitely get to know their personalities as the game goes by.  In addition to the level-specific dialogue, there are a lot of coordination comments they use, from alerting you to weapons nearby to reporting their imminent death.

I guess a good illustration of the intensity of the gameplay is my reaction to the weapons available on each level.  You always start a level in a “safehouse” — an impregnable room with a selection of health packs, weapons, and ammunition.  You can choose a single heavy weapon (such as a rifle or shotgun) to take with you, and you can’t change it until you find either another safehouse or a hidden stockpile of guns somewhere in the level.  And since the levels are procedurally generated, you don’t always get the same selection of guns on every playthrough.

In most first-person shooters I have weapon preferences — in Half-Life I’m a pretty big fan of the shotgun (if I don’t have the gravity gun) — but if I can’t get my weapon of choice, or if I’m out of ammo, it’s not a big deal.  I’ll just use one of the other ones.

In L4D2, if I don’t get either the AK-47 or the M-16 (on levels where that tier of weapon is an option) I feel naked and exposed.  It’s very uncomfortable not to have the precise weapon I’m most skilled with, and it’s just nervewracking and not very fun to play the game until I find an acceptable gun.  I think this more than anything else is the triumph of the Left 4 Dead series — that they can control pacing and atmosphere to such a degree that they can give you that “character in a horror movie” feel, just from your expectation of what’s coming next.

I’ve really only played the single-player campaign, so I don’t have the experience of going out and playing with three other guys using voice chat.  They do have several player-vs-player variants, including a very fun one where two teams of four alternate being the Survivors and the special Infected and then see which team can make it farthest through one of the levels.  It seems there’s a lot of replayability here, and I’m looking forward to giving some of those other modes a shot.

Even the single-player experience, however, was well worth the $25.  As an illustration of how procedural, dynamic content can serve the gaming experience, and as a darn good FPS game itself, L4D2 is well-worth playing if you have any taste for first person shooters — or zombie movies.

Tags: Computer, Game Review