Most of the film looks fine, but a good number of scenes have a snowstorm of negative dirt. Interestingly enough, the dirt seems to not continue through the intercutting. It's isolated to particular camera angles. That tends to make me think it might be a problem the film had on original release... perhaps some of the negative was mishandled during editing. It doesn't ruin my enjoyment of the film, but it is something to note.
That isn't the only problem... whenever there is an optical effect like a cross fade, the image gets a bit fuzzy. The stock footage reused from the original Mummy film as a flashback looks really bad. But the inserts of the stand in for Karloff and the narrator dissolved in over the top look fine, so again I think it is just sloppy editing.
The film itself is more like a low budget serial than an elaborate gothic horror film. The acting (aside from Chaney's pantomime performance) is abysmal and setting the action in a swamp in the deep South is pretty absurd. Add to that a cringe worthy performance by a black worker who calls people "Massuh" and the most unconvincing gypsies ever put on film, and you have a recipe for something destined to sit on the shelf unwatched.
If you love Universal horrors the way I do, you should probably pick this up for completeness's sake. But I seriously doubt this will ever be fully restored for release in the US. The blu-ray is region free and the French subtitles are removable using your remote control.