At the bottom of "blackjack rules for 2 players" lies a single number: the share of each stake a game keeps on average, known as the house edge. At table games it follows directly from the rules. A change in one payout or one dealer rule moves it, sometimes by more than the gap between two whole games. Knowing which rules matter lets a player compare tables in seconds and see what an hour of play is likely to cost.
Roulette shows the effect of rules more plainly than any other game. A wheel with one green zero keeps about 2.7 percent of every bet, and adding a second zero raises that to about 5.3 percent without changing a single payout. Some tables with one zero return half of an even money bet when the ball lands on zero, which halves the edge on those bets. The layout looks alike in every version, so the number of zeros is worth checking before the first bet.
Blackjack played with sound strategy carries one of the lowest edges in a casino, often under one percent, and the rules decide exactly where it lands. A natural paid at six to five instead of three to two adds more than a full percentage point on its own. Fewer decks, the right to double after splitting and an offer of surrender each trim the edge slightly. A player who guesses instead of following basic strategy pays several times the published figure.
Related questions: