I've only played it coop, not SP, so needless to say highest difficulty/100% Ghost was not even close to achievable. That said, I never enjoy highest difficulty anyway, I strongly dislike playing missions over and over and over to win or reloading it 100x to a given save to get it done.
If it's really hard to avoid detection at a certain point, screw it, let them detect me and I'll fight my way past!
CT is still my favorite SC game, though. I think this one ties with the original.
The Jedi Master