As a kid I played a lot of Wonder Boy in Monster Land on the Sega Master System and never made it past the pyramid, then played it a bunch circa 2002 and got slightly further, and finally revisited it with the necessary seriousness in 2012 and beat it.
Monster Land is a mostly linear platformer, but stuffed with hidden coins, hidden shops and hidden bosses. You can attack or press up in seemingly empty spots all over and often you’ll find something (but every level is on a timer so you can’t be thorough).
You need enough coins to purchase stuff at the shops and you need to have bought good stuff to beat the bosses, who in turn drop a lot of money. So at first when you don’t know where anything is the game seems insanely hard, but the more secrets you’ve memorized the further you get. It’s really satisfying when everything falls into place and you find a route with just enough money to buy the best armors.
Also, the final boss is invincible unless you’ve earlier beat a super secret boss for a unique item and then found a super secret shop that lets you exchange it for the spell to reveal the dragon’s true form