GNS have interviewed Charles from Hostile Intent.

Here's a snippet

GNS: Given the limitations of the Half-Life engine, what were some of the harder things to implement into the modification? What sort of enhancements were added in (in terms of aesthetics) in general?

Charles: The hardest thing we tried to implement was what we called our “supers secrete aiming system”.

This “system” consisted of 2 horizontal lines, about 1 inch apart, in the same place as your reticule is in other games. The difference is, similar to the way DOD does it, there is a little dot that moves around and jiggles according to your movement. This was to represent your accuracy and unlike DOD when you fired; your bullet was supposed to go right where that little moving dot was. We never got it to work. 3 coders look at it, tried, and failed. It never worked so we scrapped it for the iron sight aiming system.

In terms of aesthetics I suppose we have our weather system (snow, rain, fog etc) as well as our 3-year-old but still outstanding player models.

You can read the rest of this interview here