In my own opinion, modernistic literature is depressing.
More factually, though, modernism is generally associated with literature written in the first half the 1900s. The following authors are generally accepted as all being modernist writers: T.S. Eliot, William Faulkner, John Steinbeck, Joseph Conrad, F. Scott Fitzgerald, and Ernest Hemingway.
If realism was a general departure from romanticism, modernism took it one step further. The early 1900s was a rough time. Two world wars gave authors a pretty bleak outlook on the future of humanity, and their writing reflected this. Modernistic literature tends to be a bit more stream of consciousness, filled with irony or satire. Readers may feel that the story isn't really going anywhere, but that the story is focusing on the hopeless isolation of a main character. The Great Gatsby, Heart of Darkness, Barn Burning, The Old Man and the Sea, etc. all are good examples of the fairly bleak outlook on mankind and society.