It makes sense you can't crit with a heal.
Regeneration can be an attack though with undead or decaying.
Mind you it makes no sense to me you can crit with magic at all - except perhaps a staff.
I meant "sense" gameplay wise. Regeneration is a multi-turn spell to avoid the huge burst heal that would make any damage you did up until that point meaningless, because someone would just burst heal them back to full. It's intentionally designed that way, so I think critting heals (even though I am a fan of that in other games) wouldn't serve the gameplay. Maybe with a critical modifier nerf to them to only slightly increase it.
The tooltip could change to indicate it only applies to damage, they probably had that distinction in their mind during design.
