I'm not a huge fan of the 'insta-heal' magics like the Heal and Cureall spells from AD&D and BECMI/RC D&D. Using the OD&D and B/X (and Swords & Wizardry) games as a guide, Cure Light Wounds is a 1st level spell, Cure Serious Wounds comes in at 4th level (+3 levels) and is double the effect and there are no other damage healing spells available. I thought this was a bit light though. Hence, Onn's version of Cure Critical Wounds is 7th level (+3 levels from Cure Serious Wounds) and is again double in effect.
Cure Critical Wounds*
Spell Level: Cleric, 7th Level
This spell cures 4d6+4 hit points of damage or can bring a dying character to 0 hit points and immediately heal 1d6+1 points of additional damage. Optionally, this spell can remove paralysis, cure blindness or deafness but when cast in one of these fashions no damage is cured.
An evil reversal of this spell allows an Anti-cleric to cause 4d6+4 points of damage if he successfully strikes the victim with a +2 bonus on the ‘to-hit’ roll.