Imagine, if you will, this scenerio. A random bunch of strangers met up in a random location in order to embark on a dangerous journey, equipped with only what they have on hand. It's probably the start to many a RPGs and heroic journey fiction (fantasy, sci-fi, or otherwise) but it's also the start of Left 4 Dead.
In playing L4D recently, I was reminded of the Quick Start Guide for D&D/AD&D (first edition blue box for the geeks out there) as well as similar D&D related products of that time (like some of the various board game or adventure sets available). In that, if you didn't want to make a character, you basically picked a stock character and went onword. In Left 4 Dead, you do the same, filling in the background as you go between the characters.
But as this thought lingered on my mind, I began to notice how in playing Left 4 Dead, a lot of the basic ideas put forth in the Dungeon Master's Guide as well as the general ideas in heroic fiction, seemed to fit the gameplay of Left 4 Dead.
Take for instance the role of random encounters and encounters in general. In pen and paper RPGs, random encounters aren't as they are in consoles/computer RPGs. Rather than being means of generating XP and resources, they're outlined as a way of -reducing- resources. I recall one DMG mentioning that a random encounter should probably use up about 10% of a party's resources (subject to finding more potions and resting to regain spells and health, of course). In Left 4 Dead, the common infected generally fall into this part of the traditional adventure. Even in groups, they're not likely to cause significant harm unless the party is not careful. But they do force the party to spend resources - ammo, in this case, unless the party is being cautious.
In time with the common Special Infected, these produce the more story specific encounters within an adventure. These encounters generally use up more resources and are more dangerous. It's more likely that a character will be heavily damaged but the expectation is that most will probably survive.
Lastly, when you have the Tank and the Witch, these are the bosses of a dungeon or other major milestone monster. These are the most dangerous battles where every last resource is generally used up with only a little left to spare;resources you find after aren't just rewards, they're a resupply.
In a similar parallel, let's look at the advancement of power and items. In the stories that D&D draws upon and some of the original settings of D&D, the gaining of a magical item was a big moment. Generally, that item became the signature item of a character and there was rarely a time when they switched weapons or 'upgraded' or what have you. Aragorn for instance only really got one sword during the books. In Left 4 Dead, especially on the harder difficulties (or in versus on occasion), finding the improved weapons is usually a big moment (and appropiately, you're most going to find them in the mid-sections of levels and of the campaigns - you won't find it in the first episode ever). It gives the party power and confidence and a significant upgrade. And, generally, people tend to pick their favorite weapons - their signature weapon if you will.
But perhaps most of all, consider the role of the AI director as a Dungeon Master. The AI director isn't really trying to kill the players - it's trying to provide a sense of challenge and produce epic moments. It's balancing challenge and rewards and progress to create a story along side the players.
So, perhaps, as gaming continues to develop, the ideas of Left 4 Dead as applied to RPGs can help answer some questions. Approaching instances in MMOs for instance in the same manner as a campaign in Left 4 Dead might provide a way of creating a story that both fits a particular static structure while still maintaining a dynamic and personalized feel to it.