In a recent interview with Gamespot, Miyamoto said that the European version would be bigger than the Japanese and the US version.

Here's what he said:

Did Luigi's Mansion turn out to be the game you wanted it to be?

'Actually, games like Luigi's Mansion and Animal Forest, which we've just recently released in Japan, are really being driven more by some of our younger directors at Nintendo. It's not so much my vision of what the game will be--I supervise the overall development of the game. It's true that the director of Luigi's Mansion still feels that if he'd had more time, he could have put a lot more into it and come out with a better game. And so to that extent I think he has some regrets about it. '

'Though, in the case of Luigi's Mansion, for the European launch, we've added some new elements to the hidden mansion that become accessible after you clear the game and strengthened that mode so that people will probably be interested in playing it a little longer than they did the US version.'

At least once we're getting a better thing than the Japanese and the American. What the new elements will be? Who knows? In the US version you could play the whole game again, in a 'Hidden Mansion'. It might be that Nintendo made this mode more difficult. It could also of course be, that Nintendo added some mini-games. We'll see in 2 (doh!) months...

Source: Gamespot