Would it have been weird if it fluctuated based on the phase of the moon? Let's say it had all 4 stats available: Weapon Critical, Spell Critical, Critical Damage, and Critical Healing at 5% base each. Depending on the phases of the moon Full, New, Waning, and Waxing each individual stat would go up 3-5%. Like say during a Full Moon your Weapon and Spell Critical would go from 5% to 8%, Waning Moon Increases Critical Damage from 5% to 10%, Waxing Moon Increases your Critical Healing from 5% to 10%, and New Moon everything is at the base 5%, but increases your stealth radius bonus from 3 meters to 5 meters.

I know it would have been one hell of a balancing nightmare, but it would have been cool if changes like these would occur.