Indeed I think most of the units each general has have been made in some way unique from their 'vanilla' version, or even totally replaced with something more suitable for their general. For example the GLA Toxin General now has a unique, more heavily armed version of the Toxin tractor and the Chinese Tank General can build a tank bunker instead of the normal infantry bunker. Most of the new content revolves around making all the different Generals far more unique than they were in vanilla Zero Hour, and they all play very differently from each other now. In addition to all the new things added to the existing generals it also adds 3 entirely new ones- a salvage general for the GLA, a special weapons general for China and an armour general for the USA. It also fixes quite a few bugs from the original game and adds useful features. It takes the base game and adds great deal of new content, but all of it retains the same style, both visually and gameplay wise, as the original product. The basic premise of the mod is to be like an expansion pack for Zero Hour.
I have been playing it often since then and was really impressed by its scope and professionalism, so I thought I would post some info about it here so people could try it.
This is a mod for C&C Generals Zero Hour I have been watching in development for some time and over Christmas a very stable, near complete version was released.