This is a B-movie that could have been an A-movie if made eight years earlier, pre-code, with Marlene Dietrich's acting in earnest a little more complex and a little less jaded part. The grotesqueness of the characters in the perceived Wild West deprives the movie of its subtlety and hence power. Even though James Stewart is doing a good job, he is given too little work to excell.
As for subtlety, therein lies the great challenge of art. On the one hand, the work should be sufficiently stylised in order to highlight the problem that it addresses. On the other hand, the work must have enough fine detail in order for the problem thus defined to be non-trivial and the insight emerging from the work to be non-negligible.