The Evil Within just have 75 metacritic on PS4, is still in green, but it's my most underrated game by far. Its gameplay and visuals are not as polished as a Naughty Dog game, but game design, scenario, story, boss fights, set pieces are some of the best in this gen and is one of the best survival horror games ever.
But by your rules, by far the best sub 75 game this gen i've played and criminally underrated by its circunstances at launch is.....Assassin's Creed Unity (with 70 on PS4). Still one of the most gorgeus games this gen, with an ambition and detail recreating a historical setting we are not seeing anymore in the franchise. For me, it was the best old style AC alongside ACII. Its focus on stealth and how to realise how to kill your target is what i like about an Assassin's Creed game. Yes, it had bugs, yes it could be frustrating at times because you don't always do what you want to do, but RDR 2 have those same problems too and is a 97 rated game.