I think called shots at range ought to be hard. If the other guy doesn't know you are there or you are are close in, they get a lot more likely.
If you are hit in someplace particular (and most times, this is the case!), you should sustain appropriate damage. Limb hits that don't hit a major artery are somewhat debilitating, but not immediately life-threatening. If they do enough mechanical damage, they can impair motion or use of apendage. Really, you come down to having real damage include shock, damage to the blood system (ie ruining its integrity and letting you exanguinate) and mechanical damage to the limb or area in question that impedes use.
If you get hit in the head, for instance, effects could include stunning, concusions, impeded vision or hearing, loss of balance, and if the hit is bad enough, skull fractures, brain damage, permanent organ damage to eyes or ears or teeth/mouth/throat, and of course potential for blood loss issues, especially in neck hits.
If you are hit in the body, you can take damage to lungs (making them collapse or fill up, thus making cardio stuff tough), heart (well, that's pretty bad...), stomach (you can usually live with this, but infection comes and it hurts a lot), kidneys, liver (ouch... bleeding, infection... but not usually immediately fatal). Spine hits will paralyze you or partially paralyze you either temporarily or permanently and/or give you the chance to have further excercise on your part make things worse.
Shock can put you down from a small simple wound you weren't expecting or you can shrug it off and keep going through a series of fairly serious wounds. Blood loss can lead you into shock and unconciousness, or if the performations are small enough, your body's internal compensation systems can mitigate and slow the loss and get you to a meta-stable condition, assuming you don't beat yourself up with too much activity.
Detailed wounding is tough to do right... I saw games which said things like:
Head Hit: Take double normal stun type damage, one point five time lethal damage, x% per point of damage of passing out (a save to wake up after dX rounds), x% chance of vision effects, x% chance of hearing effects, etc.
This leads to a bunch of die rolling. But it makes the combat very vivid and leads to characters who aren't necessarily going to die getting a glanding shot off the skull and passing out sometimes. Or staggering around off balance and with really impaired visual abilities. That can be quite a lot of fun to roleplay!