What is the difference between generic, ICL10, and 64-bit builds?

The main difference is the compiler that is used for compiling ffdshow.ax and thereby resulting CPU requirements:

Build Bit Compiler Requirements
Generic 32 Microsoft Visual C++ i686-compatible CPU like Pentium Pro/Athlon or higher
64 Microsoft Visual C++ 64-bit CPU and 64-bit Windows
ICL10 32 Intel C++ Compiler SSE-capable CPU like Pentium III/Athlon XP or higher