I grew up in a regional city in the 90's and this show is at least one of the reasons I always wanted to live in Melbourne, which I now do. It has this off-beat almost noir quality that captures the city well.
It's about an ex-cop (called Elvis) from a well-known catholic crime family who quit the police to run a dry-cleaner, but still uses his crime solving abilities to get his colourful mates out of trouble. He lives in a deco flat in St Kilda, drives a burgundy Valiant and has a new girlfriend every episode.
I'm not into shows like Underbelly, which seem full of drama school boys pretending to be tough (although I am a fan of Blue Murder, the Boys, Animal Kingdom and others). Good Guys Bad Guys isn't like this. I doesn't go for realism, the crooks are more like caricatures.
The show also has a lot of quality guest stars like Ben Mendelson, John Waters, Sam Johnson, Vince Collismo, Magda Szubanski and others. I sometimes listen to the soundtrack in the car (which is great by the way and all Australian) and will often be driving past landmarks from the show. It's a classic.