Actually I've never finished the game completely on Hard difficulty. Not because it was too tough, I just ran out of freetime. I plan to finish it though someday.
I've beaten MotS on hard, but I didn't get all the secrets (I think I missed half of them). So I need to play through that part again. ; )
My goal was to start from the beginning, use the quicksave feature sparingly if at all possible, playing on Hard (with AI tweaks running), and getting all the secrets. Unfortunately, there are one or two secrets on a few of the later levels that I never seem to locate (like on level 9 for instance) and instead of pouring over all the walkthoughs, I just gave up and continued playing. I haven't beaten it yet, but I haven't been playing it (too busy with other things).
But it's great..