The Coen brothers can be obtuse filmmakers: operating as if to apply their master’s touch on mainstream films solely for building the studio goodwill needed to produce the films they’re really interested in making. Such is the case with A Serious Man. It’s not mainstream. It’s not even midstream. Critics will love it, but the general audience won’t see it and those who do will find it totally, inaccessibly boring. Which doesn’t mean it’s bad- it just means A Serious …