Riposte was changed as a result of the removal of Parry and Dodge from armor in Warlords of Draenor. This passive is intended to help tanking plate-wearers to still gain a defensive benefit from critical strike.
Patch 6.0.2(2014-10-14): Changed to add 100% of critical strike as Parry. Now also a Protection Paladin passive ability.
Previous version: When you dodge or parry any attack, you gain 50% of your Parry and Dodge as additional Critical Strike for 20 sec.