Designing a Solitaire Game

In light of my ever changing passions your regularly scheduled Gimme Games is becoming another changable day.

So my passion of the moment is Solitaire Game Design. Games that can be played, or are meant to be played with only one player.

In a recent post I talked about my current working prototype, the (solo) Amusement Park Builder. This game is now on version 2.2 of the rules, so that post is outdated. In the new rules the game is quite fun, I believe, but lacks a real goal beyond "Beat your high score!". I feel this is a detriment.

As such I thought I would ramble a little bit about what I believe are the principles of solitaire game design.
(Discounting electronic games, of course)

1. Firm Goals
• Less a principle of solitaire design as a principle of game design in general, a solitaire game must have firm goals. Something towards which the player is striving. While it is possible to get away with "beat your high score" it is much more engaging to a player if there is a firm end condition where you can say you won, and another where you can say you lost. 
• Firm goals also refers to goals within the game. There need to be easily measurable and distinct stages of the game from which you can gauge your performance. 
2. Luck vs Strategy
• In a solitaire game luck has a much greater place than in a multiplayer. This is because without the unpredictability of other humans to take into account, the game can become too cut and dry. This is not to say that the whole thing should be based on luck. Far from it. There needs to be a great deal of strategy as well, as the player has as much time as they would like to devote in order to develop a plan of action. A careful balance of luck and strategy is what is needed in order to truly stimulate the player.
3. Play Time
• This is the most variable and personal quality, I believe. Both long and short games have their place in the solitaire world. A 15-30 minute game is a great filler while you wait for friends to arrive, or between classes, or any number of places. But a long 1-3 hour bonanza of play time is also great for those nights where you can't get anyone together. A game that has a variable and decidable play time with a large range would be ideal, as it could fit both niches.
4. Scalability 
• The ability for a game to scale beyond one player seems a bit anathema to the principles of solitaire design, but in reality it is a major factor in whether people will play. It is much more enjoyable to find a game you really like and are good at, and then be able to share it with friends than it is to ave it to yourself forever.
5. AI
• Solitaire games are much more enjoyable when you only have to play from one side. This ties back into luck and strategy. If you have to constantly shift gears between "Player 1" ad "player 2" you have less brain power to devote to coming up with ideal strategies. Luck therefore makes a great opponent and should be used to help mitigate the brain power needed to play two sides.

This is by no means a comprehensive list, just a smattering of ideas I had while thinking about solitaire design, but it is certainly a list I would stand behind.