I remember most of my fellow pupils having great difficulty understanding his unique prose, because of the rather Biblical style and vocabulary of his Hebrew (although he is surprisingly readable despite that) . They had trouble figuring out what he was talking about. I handled the prose rather well, and did not find it too hard, probably thanks to my having read a lot in my childhood, including some old-school translations which sounded rather Biblical themselves.
But I didn't much care for Agnon at the time. His language -- his cunning choice of words, his composition, his constant allusion to various layers of Jewish thought, from scripture to then-contemporary customs -- went right by me. I did not appreciate the sheer beauty of his craft.
Last year, in Prof. Perry's course, I was required to read Agnon's פנים אחרות, a short story which Perry used to demonstrate some of his theories of analogies disguised as metonymies. Reading it was discovering Agnon. My current appreciation for and fascination with language simply did not exist at 14, and my sound chamber for language was still rough. I resolved to begin reading Agnon's massive oeuvre, but of course found no time to do so yet.
Last week, Prof. Sternberg assigned Agnon's בדמי ימיה as one of the books we shall discuss in his remarkable Introduction to Theory of the Novel (although it's not a novel), and I've just finished reading it. The sharp reader will notice that this is one of the Agnon stories I had read back in junior high. I actually remembered the basic plot, but had no recollection of the lyrical beauty of the text. Rereading it was actually reading it for the first time with appropriate capacity for the story. If you can1, read Agnon!
...and immediately I think of my younger siblings, who can't enjoy Agnon today (they have far weaker Hebrew than I had at 14, and little interest in improving it, alas), and who probably never will. This saddens me.
1Hmm. Agnon in English? Scary thought. But Google suggests that several books (only a few) were translated into English. So I guess you Anglophones might try them, but I can't guarantee the magic in English.