I think this would add some interesting dynamic to the game. Although as you say it increases the complexity of the game tremendously. The head, torso and legs separation seems like a good balance point though. But it really depends on the game design, breaking your legs is game over in a platformer if you don't have some interesting mechanics when that happens.
Maybe the player would need to defend him/herself from enemies while not being able to move when having broken legs for a while, and having the leg health automaticly regenerate.
You could also get different disadvantages depending on where you're hurt. Lets say there's three damage stages:
Normal - Everything functions as intended.
Hurt - There are some disadvantages. If your head is hurt maybe you have decreased vision, are confused etc.
"Dead" - Torso and head damage here would be fatal but damage to the legs may result in the scenario I described above.