How would a black hole effect us?
It would bring an end to our solar system.
If a moderately sized black hole crossed through our solar system the results would be cataclysmic. Even before the black hole entered the solar system, its enormous gravity would start effecting everything.
The black hole's gravity would first be in competition with that of the sun's gravity. The orbits of all the planets would first become more elliptical than they are now. As the pull of the black hole grew stronger as it got closer the competing gravities would cause the planets to become misshapen, distended.
If the black hole had enough mass it would eventually pull all the planets into it and finally pull the sun into its center.