He didn't become infected until the end of RE1, but up to that point he wasn't really a normal human either. The C:V thing was all part of his infection post RE1.
Krauser has a severe weakness to flash grenades, knifing, and being shot in the feet. I died a bit more frequently to that experimental ganada.
He does, he just chooses to ignore it. Considering that RE started as a bad zombie movie and later became a bad action movie, I'd say the films are plenty faithful.
