If we figure out why people play differant game types......

I'm not sure how much help I can be to your project, since I'm not sure how one gets from being able to classify games to being able to create them. (Step 2: then a miracle occurs...). However, your thread did suggest an idea that I thought I'd share.

I propose that it might be more challenging and potentially productive to make a list of types of games that DON'T exist, and look into why not. For example, with all the cooperative games that have come out since Lord of the Rings, why has no-one made a two-player cooperative game? It seems like there would be a substantial market for such a game, so there must be complicating factors...

You cannot really classify games, neither can you do it for people, books or other variable stuff.

Look at board game seek, there is probably more than 100 game categories and there could be many ways to reorganise these game categories according to various taste.

For example, in a library, there is the dewey and the library of congress classification system. But I am sure that I can successfully find a book that does not fit in any of theses(ex: an RPG book).

If you want to know which kind of game people play to know which kind of game to make, I think that you should focus on game elements. Does the people play social games, abstract/themed games, complex/simple games, etc.

Actually, there's a subtler reason based on "learned behaviors" and conditioned responses. It's easier to see in animals because we humans like to think we're rational, but it really does work with us too.

If you want an animal to learn to do a trick, you reward it whenever it does the trick successfully. If you reward the animal every time it does the trick, it will learn quickly... but if you then stop rewarding it, it will also forget quickly. But if you reward the animal only every few times, and somewhat at random, the animal will learn slowly and also forget slowly when you stop rewarding it.

So: design a game that rewards a player with something cool every couple of turns, especially if they can be other player's turns as well. The rewards should be frequent but somewhat unpredictable. If the game itself is fun, it will have the additional quality of being addictive -- or at least, habit-forming. People will continue to play because the frequent-but-ragged reward system conditions them to keep playing. This is one reason why so many video games are popular: every few seconds, you get a couple of points, or blow something up, or kill a monster, or achieve the next level.

I don't say that this is the only factor in making a popular game -- far from it! -- or that all popular games have this characteristic. But it's one that can help keep players coming back for more.

I think that this comment may be more vital to explaining why we play games than we may think. Think about it. The REASON why we play games is simple, we like to have fun. Fun though, is probably one of the most subjective concepts on the face of the earth. So what we as designers try to do is find something that we find fun, and present it in a way that others will find it fun as well. But the problem in establishing codes of conduct or specific "why" reasons in gaming is that you could potentially have the most awesome concept in the universe, but if "player A" would rather play go fish, then to him/her, the concept is lost.

What Larienna touched on was the fact that when you think about the elements of the game, you get a glimpse into the personality of the person playing. For example, some people can't get enough of party games. Scatergories, Taboo, Pictionary to name a few. Look at what these games have in common. They don't require a ton of knowledge or experience. They usually spawn inside jokes. They are easy to learn and are good ice breakers. Now see if you can figure out a personality profile for the people who favor this type of game....

I look at games as a medium for human interaction. Being with and interacting with other people is fun, and we don’t always get to interact with people in the mundane world in the ways that games allow us to do. When was the last time you were at an auction, or bargained with someone for something, or decimated someone’s army with your superior strategy, or stole from them or bluffed someone, or competed with or really cooperated with someone for that matter. A lot of these activities seem to be built into our human nature and are pleasurable. Although they can’t be part of our lives all the time since we have our real-world roles to fill they can be part of our lives in game form. I know this doesn’t directly address your question, but it’s the way I look at it.

I think the only real accomplishment, I feel, is that I had some fun and maybe outsmarted someone else.