Difficult: Play across multiple difficulty modes, including the one hit kill Nightmares mode. (digitalchumps.com)
While you could certainly rush through the main game in around five hours the first time around, you do have multiple difficulty modes on offer, with one unlocked after completing the game on hard. (thesixthaxis.com)
As far replayability goes, props to the developers for including multiple difficulty modes and leaderboards for those that like to compete for that perfect score. (thevrgrid.com)