Occasionally exotic but sometimes just one long march, Thierry Michel's "Congo River, Beyond Darkness" plunges the viewer into a two-hour trek up the 2,500-mile Congo river from its mouth to its distant source. This exploration of post-colonial Africa is full of riches for viewers patient enough to complete the journey. But lacking the ironic focus of a "Darwin's Nightmare," this mental safari will mostly be made by small-screen travelers. This is the fifth film Michel has made about the region, beginning with his 1992 "Zaire, the Cycle of the Serpent." As he browses among the people who live along the river, he underlines not only their profound knowledge of their country but the poverty, war and horror they have survived. The filmmaker's own deep love of the land draws the viewer into their complex, post-colonial world.