Complex damage is good, but I'd just make sure it doesn't slow down combat more than it has to. WT is my favorite hit locations system in that regard.
After some pondering, quick idea for a model.
1d10 rolled to resolve; 7-9 succeed, 10 is additional success, and 1 a horrible failure.
Deal with tissue layers as main focus with bleeding as a secondary. Hit locations aren't mechanical but narrative to explain locations of injury. Remove "called shots" in favor of all attacks being targeted to a location, ie "I swing for his head" instead of "I attack".
Attack success is automatic unless prevented. Defender rolls to evade. On success the Defender avoids damage. On a failure the Defender can opt to change what is struck within narrative reason ("I hold my arm up to protect my head"). On 1 the attacker gets a clear shot.
Damage is 1d10 with static bonuses for more harmful weapons (+2, +3, etc).
Injury is tracked in two manners: vital area and non-vital area, with damage values attached to each layer. Layers are tracked in three dimensions.
Non-vital areas (arm, leg) are skin(1), muscle(2), bone(4), muscle(2), skin(1).
Vital areas (torso, head) are skin(1), muscle(2), bone(4), vitals (1), bone(4), muscle(2), skin(1).
If someone is wearing any sort of protection then that must be penetrated prior to skin, ie Big Fluffy Jacket(1).
Damage is "absorbed" as it passes through each section. So if an attacker used a knife (+0 weapon) to attack someone and rolled a 2 for damage the attack would pierce the skin and into the muscle but not reach the bone, a 'flesh wound'.
After being wounded the victim begins bleeding. All normal characters have 100 blood points. Bleeding each action is equal to layers penetrated squared. Each wound is considered seperately. So the stab above would cause only a single point of bleeding because only 1 layer was fully penetrated. Characters suffer cumulative penalties at 50, 25, and 10 blood points. At 0 blood points a character dies.
Any wound that did not damage vitals can be bandaged or otherwise treated to slow or stop bleeding. Damage to vitals requires special measures.
Some blood points can be restored by replacing blood value and hydrating with water or juice but mostly it takes time.
The base system seems pretty horror gamey. By adding more ways to protect one's self or increase location values it could get much more action centered.
Big flaws? Thoughts? Condemnations for stealing other people's ideas?