I'm sorry, I'm not sure which game you mean, but I'll spam a list of all the freeroam games I know, maybe it helps:

Total Overdose

The Godfather

Boiling Point

True Crime New York City

Gun

True Crime Streets Of LA

Mafia

Scarface

Driver 3

Driver Parallel Lines

The Getaway

Mercenaries

Destroy All Humans!

Saints Row

Crackdown

I can't really find a game fitting your description (casino missions), but maybe I was able to help at least a bit.

This game has been announced a long time ago.

It is the sequel to "Gangland", you should check it out.

www.2moons.acclaim.com

Just got released, I'm trying it out too.

Older games like Sanitarium, Phantasmagoria or Harvester tended to be quite sick.

Newer games just go for the shock and thrills, games like:

Postal 1&2: Just a sick idea in total ( I liked it though )

Manhunt: Whatisthere left to be said ( I liked it )

The Suffering: One of the best modern horror games. Bloody and scary ( I liked it, what a surprise )

SoF 1&2: Good splatter,, but was too simple for me ( Didn't really like it )

Prey: Nothing special, just the organic feel.

Bloodlines

Scarface

Total Overdose

Gangland

Boiling Point

The Suffering

The Punisher

Stubbs The Zombie