The summary.
IF THE CORE LOOP IS NOT SATISFYING AT ITS SMALLEST SCALE, NOTHING BUILT ON IT WILL BE
Build it and play it hundreds of times with no content. Depth means simple rules producing complex situations — not many rules.
Remove anything players do not engage with; every system costs attention.
DIFFICULTY SHOULD COME FROM DECISIONS AND EXECUTION
Not from unclear information, unfair surprises, or randomness the player cannot influence. And failure should teach something and cost little time.
IF NEW PLAYERS DO NOT UNDERSTAND, CHANGE THE DESIGN RATHER THAN THE TUTORIAL
Introduce one mechanic at a time, in a safe space, before combining it with anything.
Appearance must match function, or players learn not to trust their reading of the world.
VARIABLE REWARDS ARE THE MECHANISM BEHIND GAMBLING
Which is why systems designed to compel rather than reward deserve deliberate caution.
BLOCK OUT LEVELS IN SIMPLE GEOMETRY AND PLAY THEM FIRST
Layout problems are cheap to fix before art and expensive after.
WATCH PLAYTESTS IN SILENCE, AND NEVER ASK WHETHER THEY LIKED IT
Players reliably identify problems and unreliably identify solutions. Test the first ten minutes most of all.
