While there are upsides to compulsory voting this is one of its downsides IMO. Because you can't "refrain to vote" the parties know all they have to be is slightly better than the alternative and they will get your vote. In some ways it entrenches the two-party preferred system and means they only have to differentiate on minor issues. In the end they don't have to be good to get your vote, they just have to be slightly better than the next party in line.

If you are not satisfied with either party you still need to vote. Even if you vote for a minor party you know many who aren't as engaged in politics will vote for one of the two majors anyway on relative, not absolute basis limiting the power of your "politically engaged" vote.

That's my impression of Australia's politics. There's no perfect system.