Based on experience in other games I'd expect it to work one of two ways:
Crit: ( Damage + ( Damage * Bonus damage percent)) * (2 + critical damage percent)
Crit: Damage * (2 + critical damage percent + Bonus damage percent)
If it works the first way, then % crit chance, % damage, and % crit damage are all multiplicatively more useful together, and it behooves you to get some of each. If it works the second way, then everything is simply a percentage increase of your base damage, and relatively interchangable.
Other orders of operations tend to be counterintuitive, but are not unheard of.
The Amalur wiki currently being one that speaks in general terms instead of hard math, does anyone know the exact order of operations?