information over-saturation

Due to combinatorial explosion, a linear increase in options creates a non-linear effect on decision-making. So, ReneWiersma is absolutely correct about limiting the options you give people.

American style games typically resolve this problem by eliminating choice altogether. You've got the hand you're dealt (or the card you draw), and it's up to you to figure out how to make the most of it. Fortunately, with this type of dynamic, most of the combinatorial explosion occurs in your hand so you have everyone else's turn in addition to your own to figure out how to manage it. Also, if you notice, most people sort and order cards in their hand. When confronted with more than five or so options, people develop a system of organization (all the same suit, all the same numbers, 'sets', etc...) to help them see patterns in the mix. So, I find that whatever you can do to place the problem of choice into the player's hand, the better your game will flow.

I think the worst thing would be to have a dozen cards on the table each with four or five properties which operate at cross-purposes (dimensionally orthagonal) to each other. In that situation, even experienced players will find themselves stuck by considering their options.

Whereas ReneWiersma points out the rule of 5 for options in play, I abide by the rule of 3 for the information on the card. I try to avoid having more than 3 different dimensions on a card. Perhaps it has a cost, a strength and a special effect. Or it has a number, a suit and a rank.

Think of poker, each card can either be used in a flush, a straight or a set based upon its suit and number, but the higher the number (it's rank) breaks typological ties. The interesting part of poker doesn't necessarily come from the cards, but from the rules that keep each player from knowing for sure what other people have and the huge variety of possible recombinations of cards that may allow a nothing hand to become a winner at the turn of a card. Having a number of different dimensions allows this dynamic recombination, but each dimension itself is extremely simple and intuitive. Hence... poker's broad appeal. That, and everyone's innate desire to gamble.

A way to have a high amount of information on a card but keep decision making down is to reduce the amount data that would have an effect on that particular decision.

For example, if a card can have 5 completely different and potentially complex effects in the game, and a player has to choose a particular one out of a selection of 5 - that could be 25 unique pieces of data to sift through - which would be a daunting task - however if the player is forced to use that card in only one of those ways - then only that piece of information matters - while still serving duties in all of those particular ways.

Say you had a game in which there are 5 ways to act - a build action, a payment action, an instant action, and a response action, and a score action. And cards had between 3-5 effects each working toward a separate action. You could have 5 cards face down in front of you each specifically dealing with that action. When you chose a score action you would get a greater effect from that action and other players could play a card from one of their spaces to ride on your score action - and then each player could draw 3 cards - and do a quick once around the table draft to replace the card they had played. Each player would be looking for a card that would maximize the role of the card they just played, and thus would be less interested in the other effects of that card - reducing relevant information (at a beginner's level) to one piece of data to evaluate from those three cards. At an intermediate level, they would also check (if sending left) the effect of the card the player to their left needs to replace so as to make sure they are not passing a card that would be too powerful to that player. And at the advanced level, you would be making sure that if the card made it around to the leader, they wouldn't advance their position too far, the person on your left wouldn't want the card - and the other effects of the cards you were drafting could be used as solid riders. As you reached those higher levels - then you would already be more familiar with the cards and the decisions would be less time consuming - as -for the most part- its that primary effect of the space you are filling that has the largest impact on the game.

So really it depends on the game mechanics. Cards can have a lot of data but as long as the amount and types of data you need to deal with is relatively small, or else easily pared down it doesn't have to be overwhelming. But if a player has to deal with potentially (in the above scenario) 15 unique and equal pieces of data - that might be overwhelming and lead to random choices. It all comes down to the design.