It’s very similar to San Francisco’s Tenderloin district.
It was the low-life capital for many decades, then became a sort of sleazy nightlife capital for a few more (the place to go for nightclubs, but also for prostitution, drugs, organised crime, etc.) and while all of that’s still about (it’s got a fascinatingly high concentration of strip clubs, for example), the suburbanisation of Sydney and the influx of ethnic crime centred in other areas has dulled the lustre somewhat since the '80s.
Additionally to that, its proximity to the city and very-high-tone addresses such as Potts Point mean that gentrification’s creeping in.
If you want to organise a buck’s night that takes in a couple of strip clubs, a piss-up and a fight at the Bourbon & Beefsteak Bar (now renamed the Bourbon Bar, I believe), a negotiated liaison, a couple of lines of coke, a piss in a doorway and to finish the night off with a kebab or a pizza slice at five a.m., the Cross is still your best place to do it.
But if you wanted to go to a high-end nightclub, buy a kilo of H or pay off a cop, there are better places to do each of those things these days.