One trap that I still find super easy to fall into at times is one you may be falling into yourself: you mention that 'lack of ability to see %s' as a short-coming...but it's not. The more numbers and statistics you throw at a player, the more restricted your target demographic is (i.e. what players will find your game appealing).
This is how I'd do the damage indicator (again, very much like FO3).
- Body silhouette where base-color indicates healthy and red (varying over brightness) indicates damage.
- Hover the mouse cursor over a body part to get a status report and perhaps percentage. (E.G. minor fracture, 60% healthy-ness, whatever)
- Perhaps an at-a-glance health bar for each part (which is a direct rip from Fallout 3).
A very effective style choice FO3's design team made was to have the silhouette have a face which varied between Happy! and Miserable! (in a cheeky way) with the overall amount of pain the body was in.
All of this assumes that damage to a specific body part has a very real and intuitive in-game effect. Damaged legs slows your movement, damaged arms hurts melee damage and attack speed, and damaged head blurs your vision and hurts your aim. Things like that. There's no reason for such a fancy indicator scheme if the issues have no in-game effect. (Which you seem to be clear on, but I felt amiss not adding it, haha.)