I agree with the above two posts that with Joyce it is usually a case of simply having to "get into" the idea that the author is writing about. I don't think that either of the two works you mentioned were unreadable, but more that your friend didn't get into the author's style, and was deterred from it for this reason.

But in some of Joyce's works, most notably Finnegan's Wake the language is almost made up and therefore incredibly frustrating to many readers. Wikipedia calls it "idiosyncratic language." I like to think about it as if he is writing in an Irish bastardization of English, or that he is writing as things would sound with an accent, but it is is so different from the norm that you have to think which word he is trying to get you to read. Here is a link to some excerpts of Finnegan's Wake, hopefully it will help you see what I'm getting at.
http://instruct.uwo.ca/english/454f/fw1.html

Regardless if you're interested don't let the bad reviews turn you off from Joyce. he's brilliant and if you have the time to get into his work, you may like it. But it's definitely not a quick weekend read, it's something you have to devote some time into not only to enjoy it but to get it.

I've read some of his works. It took me awhile to understand that I was reading someone's thoughts as if they were occurring at that very moment. All the clutter and chaos of being inside someone else's thought process. I came to enjoy them better when I finally "got" that. But I can't say I really enjoyed them. There is one of his works - "The Dubliners" which is a collection of short stories. These are excellent stories with a theme and a more traditional narrative and in writing them, Joyce didn't use that "being inside someone's head" style of writing. To me, "The Dubliners" was much easier to read and understand and enjoy that the ones mentioned in your question.

I would compare Joyce's writing to Shakespeare in the sense that his work takes a bit of time to "get into." However, once your brain adapts to his style of writing, you'll be impressed. People find it difficult to follow because it's different than most writing; it really makes you think. His novels don't follow the typical linear flow of fiction writing. There are hidden meanings behind the carefully chosen words and phrases that only reveal themselves after multiple readings. Joyce's writing isn't for everyone, but I disagree with people who hold the belief that he purposefully made his work obscure and out of touch. I think his true aim was to make people analyze and delve deeper into the written word. Ulysses is one of my favorite books, and I wish more people would give it a chance. It's worth the patience involved!