What differentiates them?
Social justice/welfare and environmental action in general. One of the Coalition's main economic policies this election is to cut company tax by 5% over time while Labor is committed to spending more on hospitals and schools, and re-introduce a carbon tax (they never use the "t" word, but it is). Labor will also introduce a Bill to legalise same-sex marriage, while the Coalition has bowed to it's rural rump and will hold an expensive and divisive plebiscite.
Both parties have fairly extreme factions, from old-guard unionists on the Labor side, to troglodyte bible bashers on the Coalition's. But these factions, while getting minor concessions, do not control the policy direction. Few people see both parties as identical, and can see and evaluate the differences. They can be different without one being far left and the other far right (and I know you didn't exactly say this).