Any game which deals with a story-- a plot-- is going to have a problem with linearity. Linearity is when the player has no real choices as to what happens next in a game. Either he or she gets to the next part of the story, or finishes the steps necessary to get there, but he or she can't skip to some other part and then come back. To be fair, a story is a linear medium, but what are the compromises a designer has to tangle with?

This is a common issue. How can game designers bring the depth and emotion of stories into the non-linear world of gameplay? Well, I don't have the definitive answer to that, but I'll offer some thoughts on how to offset strangling the player in linearity and still maintaining a coherent plot.

The choices available to a designer depend a lot on the game: is it based strongly around story, or is the story only a way to string along diverse missions or other game sequences? If it's the latter, then the typical "branching" story seems to work fairly well, and since my experience does not lie in that type of game, I will leave my comments at that.

For a role-playing or adventure game, where story plays a central role, there are a few things to consider.

If the story is by definition linear, then what other ways can the designer bring nonlinearity to the player? One way is random encounters, even random quests and events. Combat seems to hold some promise in that regard-- the elements making up the combat segments (what weapons are available, what skills affect combat, what enemies are around) can be shuffled to pull the attention away from the linearity experienced at plot-points.

But these are relatively weak alternatives. A much more ambitious idea is to create a set of plot "nodes," and for each node, define how it relates to another node. By so doing, you can piece these nodes into a "web" in any order to create a sense of sequence to a random plot. This was suggested by Chris Crawford fifteen years ago, but I have yet to see it realized.

Maybe there is a middle ground here? What if we construct the plot such that the player can approach it from several points without sacrificing the continuity? This idea is not really new (and to reference Chris Crawford again, I think he explicitly mentioned this method long ago). Essentially, the player has several paths to follow in reaching the major points, and these paths can be followed in any sequence and to any extent. All paths "converge" eventually on major points in the story, but that weakness is lessened so the player may only experience the linearity at the major turning points of the plot. It's sort of a "smoke and mirrors" trick, where things don't feel as linear as they really are.

A solution I'm exploring for my current design is a little more complex. It requires a lot of "plot state information" (a history of events and actions) but might allow the player to feel like he or she has really made a difference in the plot. For example, killing a key character that has a role later in the story will change the outcome of that part of the story. The same effect might be achieved simply by angering a key character to the point that he or she refuses to be of assistance at a critical time. The basis of the idea is that the story is mapped out with all these possible alternatives (which requires a pretty dynamic game engine I might add), and the player determines which path to follow by actions and behavior rather than "selecting" a path according to what's available at any a given point in the plot. It's an advanced form of the technique of converging paths, mentioned above.

So let's be honest, there's no way to tightly control balance in a game without some linearity. If you can't predict or control how powerful the player character will be, or what items he or she might have, then you can't construct a game segment to match his or her capabilities properly-- that leads to imbalance and potential for ruining the gameplay since the player could walk through with ease, or find it impossible to beat. That balance is essential for creating a constant challenge with the right amount of reward for the work, so it can never be sacrificed, even if that makes the game linear.

As the current state of game design "technology" exists (ie, the techniques used in games today to avoid these inherent weaknesses), there's just no way to avoid linearity in story-based games. But there are many ways, well beyond what I mentioned here, for eliminating the glaring fact of linearity.

But not to forget, there's nothing bad about linearity. And really it boils down to linearity vs. replay value: there's no evidence that linearity equals diminished replay value, if it's a good game. How many times have I watched Jonny Depp's Deadman and seen something new? It's a wonderful movie with many layers of complexity and demonstrates that any form of entertainment with linearity can be re-experienced many times-- if the experience is deep and fulfilling on more than one level. If you reward players in more than one way, they will have reason to explore your creations more than one time.