One of the problems is that 'multiculturalism' is a buzz word, and politicians love them because it makes them seen in touch and trendy.
So to decide if the 'experiment' is working, you need to examine if it actually is an experiment, and what sort of results - if any, you can expect, because experiments produce results - or should do.
As I see it, if you think that 'multiculturalism' means that everyone is going to wholeheartedly embrace one hundred per cent of the culture of their adopted country, then you are doomed to find failure, because that flies in the face of human nature.
If you are hoping that each culture is going to maintain the majority of its own customs, while accepting other lifestyles and endeavouring to fit in where to do so avoids friction, then you have more of a potential for success, but again, it depends on human nature which by definition is fluid, and will not bend to fixed concepts and ideals designed as vote-winners.
I think the fault likes in the fatuity of the phrase, and the attempt by politicians to try and force cultural changes on a society which would not accept them anywhere in the world - and the result is that - as defined, the 'Multicultural Experiment' was always doomed to fail.
If you look at it more accurately, as bodies of people learning to accommodate each other and rub along well for most of the time (no snappy media buzz word there Minister!) - then that is what we have got, and have always had since the dawn of history.