I generally play RPGs as the DM/GM/Storyteller. I enjoy the role. I enjoy facilitating the story arcs for the developing characters. My campaigns tend to be focused a little less in combat and more in character development, and fortunately, I've always had players who follow suit. For us, the story is the main emphasis about the game. As such, character arcs are very important. I doubt that there is a single character in any of my campaigns that did not have to struggle with moral and ethical decisions as the meat and drink of their arcs and development.
With our focus on these aspects of gaming, a vibrant world needs to be our backdrop. I've always kind of hated player made worlds because, ultimately, they lack detail--or at least publicly understood and known detail. So my campaigns always tend to either fit in pre-made system settings, such as the Forgotten Realms, or have followed (and incorporated) real-world history and setting for "Earth-based" games. The reason why I have always used these settings is simply I want the players to be familiar with their world and don't want them to be surprised by it. The characters live in their world and should be aware of it. As a player, nothing would infuriate me more than half-way through a campaign discovering that Giants were wiped out a century ago when I was building my character to become a Giant-Slayer. Or my character building with a goal to be a dragon slayer suddenly realizes that, in this world, all dragons are friendly and immortal. Or my cleric suddenly finds out that, well, his god is kind of a dick. So I use established worlds so that my players understand the basics and the histories of their stage and setting. My biggest fear in creating a world for my campaign setting is that I would create a history or relationships that were assumed to me and would be a surprise to my players half-way through the game.
Microscope is a game about building worlds and histories.
That is a little generous. It is difficult to really call Microscope a game in the basic understanding of games. It is more of an experience, or activity. Or perhaps an exercise. Microscope does not have any winners or losers. In fact, the game also does not have a defined ending. It could play on infinitely. However, the reality of it is that it ends when the players are finished.
The game begins with defining the Big Picture. This will be the history that you are exploring. These concepts are generally defined in a single sentence or two. It could be "The Rise and Fall of an Ancient Empire", or "Man's Colonization of Their Solar System". It is this concept that you will create a history for.
From there, you create Bookend Histories to signify the starting and ending Periods. They will become the first and last Period in your history. They are agreed upon by the players and are assigned either a light or a dark tone, meaning are the events of that time generally happy or tragic. You will ultimately be determining the history in between these Periods. For the Colonization of the Solar System, the staring Period could be "Apollo 11 lands on the moon". We are then starting with real-world history and likely assign it with a light tone. The ending period could be, "Man flees its dying solar system" with a dark tone.
After that, players create a Palette for their history. The Palette consists of things that either can be included or are banned for being included. They are not to be the obvious ones, such as using a real-world setting and banning magic. But rather, there are things that should not be obvious, but will direct the histories. For example, setting a game in a fantasy world but banning dragons from the Palette, or including technology in it.
The last portion of the set up is the First Pass. Here, each player will add a new Period between the Bookend Periods or they will create and Event under one of the existing Periods. Periods are generally just large chunks of time unified by a singular theme or event--usually representing decades or even centuries. A period could be "The Reign of King Lucius IX". It is chosen to be either light or dark in tone and the player places it gives a little description of the Period. Events are specific things that occur during a Period and also have a light or dark tone. They are placed out under the Period to signify where they occur. Events under the above Period could be "Prince Lucius IX murders his father to ascend to the throne", or "Lucius IX marries Queen Alacious from the Stonewall Kingdoms". Multiple Events played under the same Period are arranged in chronological order.
Once this is completed, the game begins.
Each turn, someone begins as the Lens. The Lens chooses a Focus for the round. The Focus will be what everyone will be, well, focused on for the turn. A Focus is simply an idea that a player wishes to be explored further. The more specific the Focus, the more detailed the history will be. For example, wanting to Focus upon, "The first Tournament of Champions held by the King" will give more specific and detailed responses than placing the Focus as "The Slavery of the demi-humans". However, both are equally valid, depending on how detailed you want to be.
After the Lens determines the Focus, each player adds a Period, Event, or Scene that in some way relates to the Focus for the round (also choosing if it is light or dark in tone). If a Period is chosen, it is placed between two existing Periods to where it should be chronologically. If it is an Event, it is placed under the appropriate Period chronologically. Scenes are very detailed looks at certain Events. When someone chooses to add a Scene, they choose a Question to answer. It could be something answering motive, such as "Why did Prince Lucius IX poison his father?" It could be used to describe more general feelings and reactions, such as "How do the trade merchants feel about Lucius IX taking the throne?" It could even be unimportant to the grander scheme of the Event at hand, but could still be interesting to the players, such as, "Did the assassinated King's wife ever admit her love to her guard after her husband's death?"
After the Question is posed, the scene is set and players each play a character in the scene. Scenes are short and really just little vignettes, generally lasting no more than a couple of minutes until the Question is answered. Everyone should be playing with the idea of answering the Question in mind. The role-play can be free-form, involving inner monologues to describe motive or narrative scenes to dialogue with the other characters involved. Once it is completed, the question is written and added under the appropriate Event.
Once every player has added a Period, Event, or Scene, the Lens goes again, getting the final say in their Focus. The player to their right then chooses a Legacy from something that occurred based on the Focus. If they already had a Legacy from a previous turn, they can either keep their existing Legacy or replace it with a new one. It is simply something that they found interested and want to keep in play and explore a little more. That player then adds another Event or Scene based on their Legacy.
After this, the next player becomes the Lens and determines a new Focus.
As I said, there is no real ending and, as the name suggests, you can use the microscope to look closer and closer at events and scenes in history. But, when players are satisfied with what they have and it has served their purpose (which may simply be having fun), the game ends.
Microscope is an ambitious and entertaining enough idea in its own right to be interesting and grab my attention. However, the open-endedness and lack of real a real game there means it probably would not have gotten a lot of play more than a cursory glance and perhaps an experimental or novelty session or two. To be honest, as much as I like storytelling and storytelling games, the structure of it is a little jarring.
However, I found a purpose for the game that has made it quite useful. I've recently been talked into (or at least inspired by reminiscing) running another role-playing campaign. I've had a couple of ideas in the back of my head for a long term campaign, but I didn't want to approach it in the same way. My 3.5 friends have moved onto Pathfinder, which is not really set in a campaign world that is very well defined.
So, I gathered my players together and we played Microscope to create the history of the kingdom that our campaign will be set in. I wanted to solve the problem of my players not knowing the history of the world that they will be living in. Microscope solved that. In fact, my players intimately know their setting's history because they helped to create it.
I have to say that I really appreciated the system as well. We started with the bookends of human races first settling the region (light tone) and ended with the ascension of the new king (dark tone). It was noted that the campaign would be beginning directly after the last Period in our history.
I really appreciated this preamble to a role-playing campaign. Everything that was placed between our bookends ended up being a seed and inspiration for me as a Storyteller for the campaign. But what also works out wonderfully is the fact that the players had their hand in the creation of the timeline and history. Elements that inspired them were placed into the world. Not only do they have a knowledge of our world's history, but they were able to include facets that would inspire them as characters to be in this world.
While Microscope has limited use for me on its own, it has proven itself to me to be invaluable as a supplemental system for the start of any campaign that I will be running in the future. What is an interesting exercise on its own becomes something of immense thematic value when applied to a campaign. I have cards full of story seeds now, inspired by the ideas that the players in my game had offered. But more than that, they feel invested in the world.
Microscope isn't the perfect game, but it is as close to a perfect campaign tool as you will find if you want to invest your players and you trust their ideas.