Solzhenitsyn left a big impression on me when I was in school. I have to be really interested in something to read it or I have to be forced to. I was interested in Solzhenitsyn so I took a Russian lit class and read August 1914, The First Circle, One Day in the Life, and my favorite, The Cancer Ward. I read the Gulag just out of curiosity later. (I did not finish the Gulag) If you are only going to read one book by Solzhenitsyn then read The Cancer Ward. Read the Gulag later if you must.
If you have a short attention span Iike I do then read One Day in the Life of Ivan Denisovich. It's a great read and only a couple of hundred pages. I couldn't put it down.