The issue with this second adaptation of The Maltese Falcon is that Warner brothers wanted to not really adapt the book; they had adapted it years before, but that was in a pre-code, early-sound era studio that was trying things out. In 1934 Hammett's The Thin Man became a big hit and clearly they saw the author name and thought they could lock in to another winning turn by, in so many words, thin-manning the Maltese Falcon.
But these are two very different modes of the author - the Thin Man is a light comedy that has some serious undertones and is commanded by Powell and Loy, and the Maltese Falcon was a hard-boiled detective story where Sam Spade has to avenge his partners murder and becomes embroiled with a host of characters - and director William Dieterle thought he could have it both ways. Certainly Warren William tried to channel Powell a lot here, and he might be good in other movies (I don't recognize him), but he's really a discount William Powell, a guy trying really hard to have that charming, sarcastic patter with everyone. The script doesn't really give the audience a break from his attitude so that when he has to play serious it doesn't stick so much.
It may be unfair at first thought to try to compare this to the Huston film since, if for no other reason, this was a world that didn't exist. The one thing that this film can possibly compare favorably is Bette Davis. It's an understatement to say she stole the show; she is having so much fun in this part and at the same time doing her darndest to uplift everyone around her. She is beaming and on fire and alive in every moment on screen and there are a few seconds where it seems like she might, might, get a spark of a connection with William. And she's in about 20 minutes of the 74 minute run time.
I think this can be judged on its own terms, and on its own it just compelling past being a typical B movie comedy-cum-thriller. All of the supporting players are trying. Sort of. But a couple of actors, like Marie Wilson as (not) Spade's secretary, are given one character trait and it is grating. The tone is all just off and it is trying to be too light when it needs some darkness or at least some commitment to the dramatics of the story. I will give one little extra point to the end of the film and again how Davis is giving an A+ barn burning performance in the middle of a C-grade production.