WHY/WHY NOT: is the narrator reliable? Is the narration effective?

Nick is a pretty credible character/narrator. He doesn't have any eccentricities and seems grounded. He was educated at the Ivy School Yale and fought in WW1. Nick isn't a character who needs anything. He seems to have enough money to settle down in West Egg. He has come to New York for work and to learn the bond business; he doesn't seem to be in a hurry to get startet. For much of the novel Nick is more or less a flat character. We can see life in East Egg through him. Nick observes situations without giving judgment: until near the end of the novel. This allows the reader to trust Nick as a narrator and character in the novel.