"The Crucible" - we did that at school and I thought it was an interesting book, but I certainly didn't get why it was so powerful. And I only really appreciated Shakespeare when I've seen it acted out as it does nothing for me on the page.
That being said, we also did "Oliver Twist" and "Great Expectations" at school and I still don't get what's so great about Dickens. Is it just me, or did he really just write over-sentimentalised pap?