Nowadays, probably none. Games are much more easy now than before. Saving everywhere, 15 levels of tutorials...
But in the old Nes and master system days (and SNES and Genesis too to some extent), tons of them! More than 90% of them, to be precisely. I even emulated a lot of them and played with snapshots just to see the freaking endings! I mean, it's impossible for me to beat Ghost's and Goblins or Aztec Adventure, or Ecco the Dolphin, or Gaiares...