Currently one can only know that they have dealt a critical hit if they closely watch the damage they deal. It would be nice to have a more explicit message in those cases, something like "You hit a sensitive spot! You dealt 20% more damage this round. You hit Brigand in Agility for 6.7%."
As a side note, it would be nice to adjust the copy a bit, since normally one doesn't hit people in Agility or Stamina, rather in arm, leg, head or torso ;).