The only problem with Australia is trying to fit everything into a holiday in regards to 'What is there to do'.
For example to fly from Sydney on the East Coast to Perth on the West Coast is a 4 hour flight. To fly from Sydney to Uluru (Ayres Rock) is a 3 hours flight and 1-2 hour trip by bus.
So it really depends what you want to do and what you want to see.
You have the tropics in the north, in winter you have th ski fields down south, you have desert in Central Australia, Cosmopolitan dining in the main cities of the east coast, Theme Parks on the Gold Coast, great beaches on any stretch of coast line, history in Sydney, the Blue Mountains west of Sydney.
You can cycle, bike, hike or drive.
You can get pissed on every street corner, or stay sober, throw a shrimp on the barbie.
You can go wine tasting, bungie jumping, rafting.
Great zoos in Sydney (Toronga Zoo), Dubbo (Western Plains Zoo) or the Sunshine Coast in Queensland ( Steve Irwin's Australia Zoo).
You can mince with the gays in Sydney's Eastern Suburbs, you can pitch a tent in the world's oldest National Park...the Royal National Park in Sydney's south.
You can fish in the rivers, on the beach or hire a charter boat and catch a marlin.
You can swim with dolphins, pat a kangaroo and hug a koala.
OR you can stay in your hotel room and watch tele all day if you want