I where 6 days in Adelaide and honestly it was too long for me – but I booked a 2 days tour through the hostel to Kangaroo Island, at it was absolute amazing. You never know what kind of people there are in the group and my group was really small (only 8 total) – and we were really different, different age, different culture and backgrounds, but we learned a lot about each other.
One thing is the group, another thing was Kangaroo Island, and it was great! – The nature was absolute amazing and they there are a lot of nature miracles and we saw so much wild life, penguins parade, pelican feeding, kangaroos, sea lions and much much more.
If you are near Adelaide, I can only recommend visiting Kangaroo Island and for at least 2 days – If I could I have staid there for a couple of days longer!