You want old school flaire? Change the rules, but don't tell your players. Keep it fair, (Monsters & NPCs have to follow the rules too) but keep it mysterious.
Players who know the rules expect things from the game. They expect monsters to be defeatable,(it's a game, right?) which ruins the majesty of the powerful, rare, or exotic. These players know routine solutions to problems in a formulaic sense.
Players who don't know the rules are busy spinning their imaginations, Trying desperate maneuvers, using group plans, etc.
Make all challenges dangerous. Not just dangerous in the Lost HP sense. Let the players know that there is always something to lose. Infiltrating that tomb? Put a timer on the table. After 15 minutes, The full moon rises, and the skeletal guards awaken again. Bluffing that merchant? Succeed, and he will buy that dagger at inflated prices, but fail, and he'll tell others in town of your dishonesty. Watch as the inn overcharges you, the livery 'loses' your horse.
Old school flavor lent the idea that your tools were useful, because they made the adventurer useful. Nowadays, an obstacle appears, an adventurer is assumed to have a solution for it (yeah, I totally have rope. . . ) and the obstacle is gone. If so, why have it in the first place. Old school way, they need that rope.
Have realistic, but horrible consequences. Fallen in a pit, without a good way out? They are pulled out in three days by a traveling wood-cutter, none the worse for wear besides thirsty and humbled.
Adventure was about being dauntless in the face of difficulty, where difficulty was a varied and nuanced thing. Not just a monster of the week.