The Maltese Falcon (1941):
Honestly, I might get calls of heresy for this one, but I have to call it overrated. I can respect its historical and cultural import in more or less codifying film noir, and - per usual - Peter Lorre and Sydney Greenstreet are a joy to watch. However, judging it just as a film rather than for its influence...well it doesn't really hold up well on its own merits. Up until the finale, most of what happens on-screen is discussion about more interesting things that maybe happened off screen, to the detriment of narrative cohesion.
Heck, in one scene a meeting between Boggart and two other characters (Lorre and Astor) is interrupted by the arrival of the police, who want a word with him. He steps out, and a few seconds later we hear Lorre yelp out a call for help, and they rush back in to find Lorre bleeding, and Astor cowering, claiming she hit him in self-defense after he attacked her. Lorre calls her a liar, says that she'd threatened to shoot him and only hit him with the butt of the pistol after he'd called for help. The two get into a bit of a scrap, and Boggart says that it can all be explained away, offering a somewhat slanted rundown of how he knows the two, with a reminder that he's got dirt on Lorre from their last encounter if Lorre wants to pursue charges. As the cops are about to take everyone away, Boggart basically goes "We got you good" and claims that it was all a joke at the cops' expense, presumably a pretense, but on the other hand, Lorre and Astor immediately start snickering as if it wasn't.
And that right there is basically how the entire movie plays out. Conversation, something happens offscreen, people talk about it but you have no idea whether the conversation even includes pertinent information, the veracity of what we saw/heard is called into question...and we get no context to make sense of it. You could start the movie at the finale and have lost very little. Mind you, the finale is easily the best part of the movie, so that's perhaps worth doing anyways.
I put this one in the same bucket as Citizen Kane: great watch if you're a film history buff or just want to say that you've seen it...but probably safe to pass otherwise.