Checkers

All because of one rule, the difficulty level of checkers actually skyrockets. Without that one rule, checkers would be a super simple casual game, no where near the difficulty level of chess. The difference this one rule makes is astronomical.

Checkers is a game that you can learn to play in no time. There are barely any rules and the rules that exist are all really simple and straightforward.

The rule that makes the game so interesting and complex, is the forced kill/capture/attack rule where you must attack if given the opportunity. This suddenly turns it into a game full of strategic sacrifices and setups.

Doubles kills feel great and triple kills feel much better. But when you experience your first quadruple kill (or higher) you'll know what it's like to utterly decimate your opponent strategic wise.