There's good news for Australian games, as GameSpot AU is reporting the government has declared intentions to implement an R18+ rating before the end of the year.
If you're a publisher developing a violent video game and have intentions of releasing said game in Australia, there's a good chance you'll have to bend over backwards to do so.
Valve was forced to modify Left 4 Dead 2 (they actually released the already modified German version of the game, as Germany has similar restrictions), and select scenes from Silent Hill: Homecoming's were altered to fall in line with the country's strict guidelines.
Games cannot receive an R18+ classification in Australia, the rough equivalent of an M-rating from the ESRB. If a game is deemed to fall into R18+ territory, the game's straight up banned. Gaming advocates have highlighted the hypocrisy of this logic, given that movies can be given the R18+ classification.
There's a solid list of games that have fallen into trouble with the Australian approach to classifying games on Wikipedia, highlighting the bevy of games that just never ended up coming out there.