Ken Loach’s “Sweet Sixteen” seems to me to be one of the most important British films of the last fifteen years or so, yet it rarely gets mentioned in the breath as such contemporaries as “Trainspotting,” “Hunger,” or “Ratcatcher” (not to denigrate any of these particular films). It has a raw, unvarnished quality and such an uncompromising take on its subject that is extremely rare to see anywhere in the world anymore. Martin Compston is brilliant in the principal role, and is accompanied by an equally powerful supporting cast. Even with works such as “Kes” and “The Wind that Shakes the Barley” in his oeuvre, this might well be Ken Loach’s masterpiece.