HL1 is based on the quake 1 engine. It has some bits taken from quake 2.
As for your mod, there is no point whatsoever to work on HL1. Your so called improved gameplay or physics will in no way match source's capabilities. You don't have that much freedom over HL1.
Second, your posts so far indicate that you are inexperienced with modding meaning that people won't take you very seriously.
Third, the media is quite unimpressive and newbish.