I'm seriously considering going back to the 2E MM and borrowing from it to give monsters some of their teeth back.
Medusa / Basilisk? Save or be petrified on the spot- none of this "two chances" stuff.
Hit by a vampire, wraith, or wight? Lose 1d8, 1d6, or 1d4 of CON PERMANENTLY until healed by a Restoration spell or some such. Hit zero CON, you die and turn undead. (I don't like level drain, although you could go back to this just as easily.)
Run into a ghost? Piss it off, and you get to save vs fear effects or be aged 30-80 years ON THE SPOT.
Anyway, you get the idea. Monsters and effects in 5E have been nerfed to the point that much of the game has lost its 'threat.' In 2E, a vampire is no joke- even a 'weak' one will wreck your party if the DM plays it 'smart'. If 5E, their worst attack is 100% recoverable after...LONG REST!