Win10-64 with Geforce 960.

Game loads and runs, but in-game, the round gun sight is covered by an opaque black square that is larger than the sight and blocks what you are trying to shoot. Size of the square is not changed by zooming in with the sniper sight, but you still can not see what is directly in the center of the sight.

Has anyone else experienced or fixed this?

Try running the game using dgVoodoo. I've not had that particular issue (I have 64-bit Windows 7) but I do see interesting visual glitches when I play the game without dgVoodoo. One of them is mouse cursor blocking the crosshair for example. Also the 3D acceleration seems to break graphics in several different ways so I'd suggest you only use Software rendering (in which some graphics are also broken but less than in 3D accelerated mode).

http://dege.freeweb.hu/dgVoodoo2.html