Could you be more specific? Damage may change in certain situations, but in general it's pretty straightforward. What are you referring to?
The exact amount of damage you do per-hit, per-attack is randomized within a certain range, depending on the attack. There is the possibility for crits as well, yes, which can bump it up a bit as well. Fairly standard RPG stuff. Makes it a little more interesting than doing the exact same damage every turn.