The defining feature of casual games is that they are popular outside of the niche audience of hardcore games. They appeal to popular culture if you will. Generally this means that the theme or story is accessible to a mainstream audience (think soap rather than BSG), and that the game is understandable quickly.

Note this does not imply that they are simple, or limited, or have less gameplay or story than hardcore.

They are the games equivalent of pop, where hardcore is thrash.

In the end, I think the only possible definition of a casual game is a game that is “easily accesible.” That one phrase pretty much encompasses all the features of casual games, while not pigeon-holding it to certain audiences, sizes, prices, genres, distribution models, etc.

For example, I would argue that “Super Monkey Ball” on the Wii is a casual game – but it is not cheap, not small, not targeted towards my mother, etc. “Easily accesible” covers the features that make Super Monkey Ball a casual game – small learning curve, in-complex controls, immediate positive feedback, mini-game structure, etc.

Thoughts?

I suppose bit more answers are needed to get more features. Any other comments?

In contrast, non-casual games demand long periods of frequent play. An intricate story and/or complex goals would require players to return to the game quickly — before forgetting what he/she was suppose to do. Going a couple of weeks without playing the game may leave the player lost and confused because over time the game had built up to where it is now, and some of that play history may be forgotten.

Returning to Tetris after a year of not playing would be much easier than returning to one of the Final Fantasy games after a year.

Of course this does not mean that casual games need to be super simplistic with each period of play being isolated events. Consider a game that builds up over time. I do not know if this game exists — it may — but consider a game about gardening. Each play period could be short (10 to 20 minutes) while still building up upon previous times played by planting and pulling weeds.

I often site mini-golf as the world’s most popular casual game (not video game mini-golf, but real live mini-golf).