We've not tried a physical disability in any RP character, but we've seen one used in a fantasy setting that worked well. It was actually more or less what you used as example, Brovo. The character there had severely weakened legs. He wasn't much use on foot, basically requiring aid from others to walk any real distance. Not exactly useful for adventures or combat. Until you reveal the detail that his people were horse-riders. Stick him on a horse, and he was just as good as, if not better than, virtually every other warrior among his people. that character had not only come to terms with the disability, but had in fact conquered it.

For non-modern settings, using disabilities is a perfect opportunity to bring in misinterpretation and misunderstanding. Epileptic? Frequent leeching is clearly a treatment. Partially deaf? Bats hear well. Eat lots of fried bats to cure it. Not quite right in the head? Demonic possession. Cured by trepanning. etc.