It would actually be really cool to actually be different than million other players. I think adding small defining characteristics to each character would greatly add to the gaming experience. Right, right, you can also determine that with your playing style. Adding things like running speed, endurance, precision (in aiming), technical skills, etc. would be nice. With good planning this system could be used to support more team playing, make banditry easier (considering humanity would effect on gameplay in some way) and/or help lone wolves survive better alone. This could be implemented with little "extra skills" every character would have from a chosen list. Maybe 2-5 "perks" you can add to you character, but every positive perk gives also a negative perk. One way could also be to introduce character abilities in spider graph and adding to one skill would make other skill worse. As in this example skills 2 and 6 have been upgraded and at the same time skills 3 and 5 have decreased.