Something strange is happening to me. There are classics I loved as a young adult, read in school or outside of school, but all the classics I've tried as a... not so young adult (including some re-reads) I have not enjoyed very much. I don't know why this is. I finished East of Eden recently and I got nothing out of it, even though I loved Grapes of Wrath and Of Mice and Men (both of which I read when I was around 21 or so).
For my one classic, I guess I will say To Kill a Mockingbird, which I loved as a young adult and I would like to re-read it. But now I'm afraid to, for fear I won't like it!