DOS is not pure luck. Its not like roll a d6, you win if you do 1-3. There are stats, skills, potions, environments, planning, etc that can be used to reduce "luck" as much as possible.
If luck is both ways, I think it can be ok. That is, if you can critical a monster as much that it can crit you, It shouldn't be feeling like cheated, but like fair trade, that either goes right or wrong.
Then again, how the gameply is implemented can be very important. If a failure means instant death, it might be a little harsh indeed. If it means some heavy wounds that can take time or special stuff to be removed, you still have a critical failure, (or success, whatever), but not life breaking.
Really, a question of balance and gameplay.
