This is an incredible building and I'm surprised it's not a more popular tourist attraction in Melbourne. Perhaps it doesn't market itself that well. It was used for several very important events in Australian history - in particular, the opening of the country's first parliament. The way the colour scheme has been restored to the one for that event is appreciated and it has a lovely federation feel to it.
The hall is still used most weekends for shows and fairs but I would recommend going on the tour on weekday afternoons to see it without all the clutter so you can appreciate everything a bit better.