Depends on the game. Parrying in the opening moments of Witcher 2 is a fucking pain, because it consumes 1 bar of stamina, as does rolling dodge, and you only have 2 stamina at that point, which also takes forever to regenerate. If the enemy isn't dead after 2 parries, you're fucked for 20 or so seconds because you have no way to actively avoid damage other than running away

On the other hand, the parries in the Batman Arkham games and Shadow of Mordor feel great.