There is something inescapably peculiar about a “West Side Story” in which Riff cannot snap very well. The oddness of this detail encapsulates the serviceable version of this American classic now running at the Paper Mill Playhouse. Under the direction of Mark Hoebee, the show looks and behaves like “West Side Story,” but in ways similar to fingers making a snapping motion without achieving the distinctive, percussive pop, the show never quite f…