Parry is good. Not only against armor users as Axel_Redd mentioned, but think that Mid/highs and overheads are almost 50% of the game's overall moves. The reason i picked up batman day 2, besides that is batman, is because he kept parrying my Doomsday shoulder dash LOL. So basicaly , after you've played the game enough to know every move each character has and you have mastered the Parry, you cut off the enemy's options by almost ½.
So yeah, the parry is worth using.Even more mastering....