dtgreene hit the nail right on the head (critical range: 20/x4)
dtgreene: Personally, I enjoy healing; the problem I have with healers in D&D is that healing spells (excluding Heal and Mass Heal) are too weak; they're not that useful in combat, and out of combat, it takes too many casts to bring a heavily injured fighter up to near full health. Also, the spells are touch range, meaning you can't use them when you are away from the combat (as you can in the Dark Sun CRPGs).
Healing in NWN1 is borked. Either you have "lawl I heal my squad to full health and I can do this all day" or utter garbage with nothing in between.
The obvious solution: Make low-level healing scale:
Heal light wounds: heals (d4 + 1) x level up to a low limit
heal medium wounds: heals (d6 + 1) x level up to a low limit
heal serious wounds: heals (d6 + 1) x level up to level 10
heal critical wounds: heals (d6 + 1) x level up to level 15
area heal light wounds: heals (d4 + 1) x level up to level 15 in area.
Apply these changes to negative energy as well.
dtgreene: Also, since we're talking NWN1, I can name two cleric spells that, in the right circumstance, can outdamage the spell you mentioned; Heal (if used against undead) and Harm (if used against non-undead), provided that the target is able to survive the spell you mentioned.
More broken mechanics. What the crap were the devs thinking when they made obviously broken mechanics like that? Heal/Harm could instead scale heavily with level (6-10 health per level or something like that)
dtgreene: Furthermore, Slay Living, if the target fails its saving throw, could be argued to be capable of doing more damage. (Does the spell actually change its target's HP to 0 or -10, or does it just inflect the Dead condition without changing HP? In the tabletop game, it sets HP to -10, but what does it do in NWN1?)
**** that, use Implosion.
dtgreene: There's actually another issue (though RP rather than balance) I have with the D&D cleric and healing spells; it ties healing to religion. My preferred character would be a character who uses spells like a mage or sorcerer (though perhaps with a different spell list), but can heal at least as well (preferably better, as I mentioned above) than a cleric.
I always found the lack of mage healing to be nonsensical. Given that there are first aid kits, you'd think that wizards would cash in with a dozen brands of enchanted first aid kits available in every large city. There's no reason why mages couldn't heal. Ranger loses a leg? Reanimate it and slap it back on. Rogue shatter a bunch of ribs on a blast trap? Transmute the pieces into a living metal armor construct guaranteed to work at least as well as previously (heal damage and gain +3 damage resistance for a day). Pre-emptive transmutation buffs should be a thing. A wizard who can't temporarily encase your fighter's arm in a conjured exoskeleton construct (strength +6, damage reduction +8/physical, +10/fire, +10/cold) is obviously a sham. If the rest of your squad dies, reanimate them.
Mages are mechanically impoverished in D&D. Can't wear heavy armor, low health, low base attack bonus, can't heal. Apart from a handful of exceptionally overpowered spells (Disjunction, greater missile storm, time stop, ...), they are flat-out inferior to clerics. The best use for the Wizard class: take 1 level for Arcane Archer.
NWN1 doesn't tie healing to religion. My cleric doesn't have a listed deity and is guaranteed to heal just as well as any other.