It was basically Hard Mode for us in the U.S. It wasn't what I was expecting, but it is better than nothing. Mario games should have difficulty settings to really achieve the "suitable for any player" policy... though, you shouldn't have to unlock them.
That being said, I don't usually play though the Hidden Mansion because when I replay LM, I'm just there for the ride. I'd love to play through it in the PAL version...