Genre: Adventure; drama; western
Minor spoilers ahead.
A quick interesting note is that although many scenes were filmed in the studio and elsewhere in the US< this was one of the first Hollywood films shot on location.
Some of the dialogue would have been difficult to decipher without subtitles, especially when it comes to the old prospector, but I'm just picking at nits with that one. Although I don't consider it flawless, I ended up enjoying the movie immensely, enjoying the setting pieces that they staged for the camera, the realism in meandering about the plot and some of the characters so that some may seem random and happenstance and end up having a greater significance but does not forget that sometimes, shit just happens. The director's decisions didn't sacrifice a properly structured story for the sake of realism.
Not by accident, I'm sure, Bogart's character was the most interesting. His character is the one who has the most extreme arc, starting at one point of the moral spectrum and ending up somewhere so different from where he started that if he could look into the future to see the kind of man he becomes and the kind of things he does and the reasons for doing them, I'm confident the character would feel like he's looking at a stranger.
To capture the theme in a sentence, it's about "the corrupting influence of greed". I remember I saw a Tiny Toons cartoon a while ago called "the green-eyed monster" or something along those lines. While the characters were concerned about fending off an actual monster they later come to find that the green-eyes are the eyes of jealousy/envy, and that greed has made monsters of them. Now that I've seen Treasure I'm confident it was a nod to this because that's exactly what comes across - what can happen to perfectly ordinary, perhaps even good, men, who are tempted by greed and are alone in a remote location where they are, in effect, the only authority.