But to address player happiness in a game with frequent loss, you'll need to end them on a good note. When players die in your game, use it as an opportunity to praise how long they made that life last, or offer some cool tips, or let them retain some of their items/experience gained.

Make failure funny, dramatic, or informative. Give players a glimpse at an enemy's weakness. Don't just focus on the experience of winning, as they need to always walk away feeling they've made some sustained gain. Then they'll be as happy as they are pleased.

Finding #5: Feeling in control is a significant predictor of happiness.

Reason: Ex-Federal Reserve chairman Alan Greenspan points out that the success of capitalism is almost entirely beholden to one innovation: property rights. When people feel they can trust the system and the reliability of their own actions to safely produce lasting results, they engage life much more positively. The simple word for this is "hope."

Optimism has powerful effects on our mental well-being, and since humans are ordering, rationalizing beings, we need to know that we can safely pursue an objective without being tossed around by capricious and arbitrary consequences. Studies show people are willing to pay a premium for the ability to have more choices, regardless of whether those choices result in better actual gains.

Application: Optimism is so powerful that one study showed it influenced luck. People who classified themselves as unlucky took longer to find a positive message buried in text than those who thought themselves lucky, sometimes missing it completely even when the message was in a huge font! "Lucky" people found it in seconds.

You may think you've built in many player-pleasing features, but if they don't feel it, they won't agree. Take class balance debates in World of Warcraft -- the "cheapness" many players complain about usually has more to do with feeling robbed of control (stun-locks, fears, polymorph) than actual statistical unbalance. Maximize their experience of your design, by making it accessible, not voluminous.

Great game mechanics give us hope, even when we fail. Remember how some games keep you thinking of new strategies and tactics long after you've stopped playing? Emergent gameplay evolves from optimistic problem solving. A couple DON'Ts are called for here...

DON'T take a player's powers away without a good explanation, replacement, or promise of such. DON'T give players inconsistent control schemes. And DON'T let them fail in the same ways despite their best efforts at different approaches. DON'T ever put them in the position of disgusted regret (where they feel an irreversible loss).

We have no excuse not to use this finding obsessively. Not only is it important to happiness, but it is great at generating pleasure. The parkour of Assassin's Creed, the world of GTA that is basically a city-shaped weapons locker, or the omniscient eye we have in The Sims and StarCraft, these are tools for players to act out (or subscribe to) fantasies with. They provide instant positive feedback along with long-term empowerment.

The Roller Coaster Tycoon series made it fun to be in control... of fun!

I want to clarify that giving players control is not the same as making everything predictable. Make it clear to players that something that happens against their will is part of the game, not punishment for playing in an unintended way. Remember that sneaking in something they can rationalize contributes to the feeling of control. Ask constantly what can your player "see" at this point in your game -- do they have (or know where to get) new ideas for play?

A game is a contract between a system (designer) and an agent (gamer) that asks the agent to accept the rules to get at the meat of the experience offered. The agent should be the one playing. When the designer plays the gamer, trust is lost. Therefore, rules should be consistent, and when new ones are introduced, they should nuance (not violate) what the player has learned so far. The same goes for governments.