It's definitely sad when talented people (Matt Damon, John Krasinski, Dave Eggers, Gus Van Sant) collaborate on a well-intended message film meant to connect with mainstream audiences (a la the Jane Fonda 70s/early 80s canon including COMING HOME, THE CHINA SYNDROME and 9 TO 5) and failing at that goal.
So, let's dissect some of PROMISED LAND's flaws point-by-point (plot spoilers included):
1. If PROMISED LAND was meant mostly to be an indictment of 21st-century corporate hucksterism (getting people to pay for the privilege of having their land "fracked" for natural gas), then a different director than Van Sant was needed--someone who could provide a synthesis of Alexander Mackendrick (SWEET SMELL OF SUCCESS, WHISKEY GALORE) and Preston Sturges satire/parody but with empathy. At its weakest, PROMISED LAND seems like Elia Kazan/Budd Schulberg's A FACE IN THE CROWD on Valium.
2. The documentary GASLAND at least had the potent "money shot" of water coming out of a tap; the water (with gas included) was then set on fire. PROMISED LAND instead gives us John Krasinski's crusading environmentalist (who has a Secret revealed in the third act) doing a show-and-tell-with-props exhibition for Rosemarie DeWitt's elementary school class. Not as effective.
3. Going back to point #1, the film, by going with the "what is your price"/"why can't you just take the money" approaches, is somewhat low on drama/conflict/tension. If, perhaps, the Matt Damon corporate character had developed a sort of friendship-laced-with-regret towards Krasinski (provided no third act Secret existed), audience involvement might have increased; imagine if Krasinski had taken Damon to actual farmers/homeowners and demonstrated the negative effects of fracking--then you have a movie that shows, rather than merely relying on show-and-tell. And then Damon (plus Frances McDormand's spiky-but-somehow-likable Company Person) is told by higher-ups to destroy Krasinski's reputation and neutralize his potential threat to corporate profits...major drama which would have made for the Damon-tells-truth-about-employers-at-town-vote finale much more resonant than how it plays out in the actual film.