You will not be able to determine that Gary Oldman's first film Nil by Mouth is an acted scripted film rather than a documentary.  A great film depicting a working class South London family shot in candid documentary  fashion.  We focus in on off the cuff conversations, a junkie's (Charlie  Creed-Miles) endless search for a fix, a raging alcoholic (Ray Winstone who  also starred in Tim Roth's debut The War Zone), and their 4 generation  family.  As I said I had trouble grasping that the dialogue was actually  scripted it's so naturalistic.  Such a refreshing contrast to the Hollywood  stuff so far removed from naturalistic dialogue it has little to do with  reality.