Other's have given good synopses of the plot so I'll not go along that route, and I'll keep this brief. One other commenter noted the quality of Bill Pullman and I have to concur. He has a habit of choosing rather off-beat films that deserve greater success than they receive; I'm thinking of The Zero Effect and Lost Highway rather than Independence Day.
I was expecting very little from this film and was awed by the quality of the production. Rick managed to build its own style as a film, being grotesque and dramatic, yet the moniker of DARK COMEDY was not a lie on the sleeve, it really was very funny.
Thankfully the film only follows the same general route as the opera. Guiseppe Verdi (sounds so dull when you translate it to English - Joe Green) never wrote for the screen. Yet... the production retains a very set-like feel, as if it was taken from a play.
The only criticism that I can really level at Rick is that it seems to lose its pacing in the last 15 minutes, when you can see the slow car-crash of a finale approaching. The director really passes up opportunities to build suspense and there is a feeling of an opportunity lost. However, this stands out only due to the quality overall.
In summary, it's got really superb characters, none of them are out of the box at all. Gothic and fatalistic, funny and sexy but cruel and merciless. The acting is faultless, stand-out performances from Bill Pullman and Sandra Oh, with a special mention for one of the most cringe-worthy bosses of all time to Aaron Stanford - watch out for him in the future.