Stone's work between 1986 and 1995 represents some of the greatest stretches of any filmmaker in history and all of those films (with the notable exception of JFK) showed an ability to express the real world horrors of America's worst impulses by telling stories that were harrowing and epic in scope. Few film makers have made better long films (2 and half hours) then Stone with the notable exceptions of the usual suspects (sPIELBERG, Scorsese much of Coppola's earlier work)
The last film Stone made of any remote caliber since Nixon was Any Given Sunday. AFter this his movies have increasingly become polemics about progressive causes (W., Snowden, Money Never Sleeps) and documentaries that focus about either the left wing agenda (Untold History of the United States; everything about the JFK assassination being staged by the CIA) as well as documentaries with dictators. I'd say the War on Terror had a fundamental affect on his filmmaking but there's nothing different about these films distrust of the system that isn't in JFK or Nixon; there's just no attempt at either subelty or entertainment. In a way Stone has spent the 21st century giving America terms papers rather than entertainment.
Why such an extraordinary filmmaker has chosen to spend the last quarter of a century choosing to lecture in his movies rather than simply entertain along with the messages is one of the great bafflements in cinema history. Stone at least seems to be aware of this fact, more than other filmmakers of this type but it's still a tragedy. For a man who won two Oscars for directing before he was forty five (Spielberg was 47 before he won his first) strikes me as a man who has squandered his gift. He clearly has a lot to say about the world today, but he's apparently decided to lecture the world about it rather than provide brilliant films like this one. It's one of the great losses in the history of cinema.