I played it with Complete a little while back. It's good, but didn't make me really think it was necessary. CoP is pretty solid already so there's really not a lot for such a mod to do. The graphics are nice of course and that's where the main upgrade is. But nicer ground textures are mostly all it needed really unless you're mad for that sort of thing. I found Atmosfear spiced things up enough by itself, in looks and interesting weather.
If you're looking for something to really alter the experience in a major way it's probably not those.
There were another couple of little AI and draw distance mods I tried before, plus some others, but I'll have to check the other machine to remember.