The d20 System has several design strengths over earlier gaming systems, which make the game easier to play. They are:
- Roll high
- Whenever a player is rolling a die to do anything, they always want to roll high. There are no good effects to be gained by rolling low. Ever.
- Higher is better
- For any ability or statistic that a player has, they always want a high number. Gone are the days of trying to minimize your THAC0 and AC while increasing your hit points.
- Positive is good
- Notice a trend yet? Anything which modifies a number is good if it is positive, and bad if it is negative.
- Use of formulas
- Instead of using lookup tables for finding values, almost any value is derivable from a simple (usually linear) formula (the one exception to this seems to be max carry weight).
- Precomputability of modifiers
- Most modifiers can be easily precomputed, such that a player rolls a die, adds their combined modifier, and checks to see if the roll was high enough to be successful.