Alternate Character Interpretation: Due to the alternations to the novel's plot, there's a very good argument that Phillip Marlowe's explanation at the end that Eddie Mars killed Regan instead of Carmen is actually him doing a Frame-Up of the gangster to get the Sternwoods off the hook. Which would make him a far more morally ambiguous character.
Franchise Original Sin: Many criticisms hurled at the Genre Throwback to Film NoirThe Black Dahlia can actually be found in this - an overly convoluted story and a lot of information that's hard to hold onto. The difference is of course that The Big Sleep still has a lot of merit with regards to how well it pulls that off, whereas The Black Dahlia was a three-hour movie cut down into a confusing two-hour length.
Narm: The Adaptational Modesty to Carmen when Marlowe interrupts her photoshoot. It doesn't quite have the same effect when she's wearing such a modest nightgown.
Marlowe requests that the bookshop girl take her glasses off while they share a drink. This would be considered quite rude today.
Marlowe also wears sunglasses to pass himself off as a pretentious literature professor to Agnes - effectively invoking Nerd Glasses. Sunglasses had only just become available to the public in 1937 and hadn't caught on as a cool fashion accessory yet.
Values Resonance: Marlowe's efforts to stop the lewd photos of Carmen being made public is still very relevant today, given the scandals involving female celebrities having their private photos stolen by hackers.
1978 Movie
One-Scene Wonder: Jimmy Stewart as General Sternwood does a great performance.
So Okay, It's Average: Generally, it's a competent adaptation of the novel but considered nothing compared to its previous version.
Marlowe and other characters are open with their disgust for homosexuals. They freely use homophobic slurs like "queen" and make jokes at their expense. After getting decked by a gay man, Marlowe asserts that it didn't hurt much because gay men "have no iron in their bones."
Values Resonance: Some readers have objected to Carmen being "only" sent to a mental hospital for murder but it's very clear to modern day readers that she's seriously mentally ill and not responsible for her actions.