The only issues I have with hard core as follows.
- fall damage. being killed by falling from a hight that you would survive from in core mode. I recommend you use the lightweight perk to remove fall damage
- dying form being shot in the foot. This is ridicules even for a arcade shooter or any war game. I think for any shooter you should only take damage in the head and body, any hits you take in the arms causes you to flinch more and your movement speed is slowed down when hit in the legs. just an idea