Too many cooks in the screenwriting kitchen, from what I've read concerning the film's production.
I tend to avoid critics' reviews when it comes to films such as this, particularly when a film's advertising reeks of arthouse pretension. In these instances, I find IMDb user reviews to be much more enlightening.
It was discovered years ago by B.G. Burkett and Glenna Whitley, authors of the book Stolen Valor, that Dennehy's claims of Vietnam service were BS.