Croupier finds director Mike Hodges and Clive Owen teaming up for the first of two movies together (the next being I'll Sleep When I'm Dead) and sees Hodges returning to a form unseen since his masterpiece British gangster film Get Carter 27 years earlier. If the original Get Carter is not a familiar reference point for you, then I would advise you to rectify this immediately. If it is, then your interest in Croupier should be piqued.
I would be remiss if I didn't mention the fact that it was a British production--Film Four, to be exact. As it was produced by a British television network, Croupier does look much more dated than it actually is. British TV productions, at least up until the beginning of the 2000s, usually looked about 10-15 years older than they actually were as a result of low production value. Croupier, despite the fact that it was released in 1998, looks considerably older than it actually is. Luckily, Hodges builds character and mood so well that this flaw moves to the subconscious quickly.
Once one is able to move past this unavoidable shortcoming, it is smooth sailing, at least for the viewer's rapt attention. If you ever wondered why so many people were clamoring for Clive Owen to be the next James Bond, you need look no further than this film to see why he would be perfect for the role.