Types of Complexity
In general, I recognize three types of complexity to a rules system, and they happen at different levels and different areas of the game. There’s nothing wrong with any of them, but there’s an amount of personal taste to each of them and so you’re going to need to decide on how much of each your game will include based on your expected audience.
Mechanical complexity is directly related to how much you have to do to resolve a single part of the game. A highly complex mechanic is the D&D 3.5 grapple rules. You need to make a roll, consult the result, make another roll, consult its result, and then maybe, in three or four steps, you do what you wanted. A simple mechanic is like Monopoly’s turn structure: roll dice, buy property or pay rent.
In general, I’m an opponent of overly complex mechanics. A good game is one that I can teach the base mechanics in a few minutes (15 minutes is too long). That simplicity opens the game to the most people which in turn allows the most new ideas to enter the game. All of that is a good thing.
Being able to pick at cost what you can and can’t do sounds great on paper. I can choose both an A/C and a radio in my car, or one or the other if I so desire. Options are GREAT in real life. But they’re generally harmful to interesting game play. If you could buy any property on the board in Monopoly, you might feel better and more in control, but the game would devolve into an initial dice off, people buying as many properties as possible followed by turned of destitute land barons trying to bankrupt each other (Which I must admit doesn’t sound much different from a typical game of Monopoly!).
That said, options get complex when there are too many of them, and multiple ways to get some of them. See Item of Power in the 2nd Edition of Big Eyes, Small Mouth. It allowed you to get double the character point investment but conditional on having the item of power. So you could buy a weapon attack for 4 points, or buy an item of power for 2 and buy the same attack for half cost. This doesn’t improve the game, giving the option to take twice as many powers.
Complex choices are deciding between two similar things: two places to move, two attacks to use, two possible powers, two possible spells, et cetera. Each choice loses you something, but gains you in other areas. A great example is the game of Go. Each piece has exactly the same amount of power in theory, but where you choose to play those pieces affects the game in far reaching ways. The choice of playing in one place over another is very complex, with years needed to master the ‘optimal’ moves.
In general, I feel that choices are what should be complex in a game. The more interesting the choices, the more satisfying the game. Too few choices and the game isn’t even worth playing.
Those three types of complexity cover just about anything you’ll find in a game.
I gave my opinions above on what I feel is most important to a game, but in the end, like so many things, there are a range of tastes out there and you can’t please them all. As such, you need to pick a value for each of these that appeals to the players who are likely to play your game. If you’re selling a product, you have to keep the audience in mind.
And how about you, readers, what forms of complexity do you prefer in your systems?