I agree about Dubliners and Portrait of the Artist as a Young Man, but you can't be serious about Finnegan's Wake! That's probably the most difficult piece ever written! It's completely illegible, unless you speak 10+ languages. As far as I remember, Joyce himself spoke 13 and he was using them all in the book, making up the words combining these languages, not even to mention sentences that can span over few pages! While in Ulysses Joyce uses the technique of "interior monologue" of a consious man, in Finnegan's wake he tried to do similar, but for an unconsious man (= in a sleep)! I fluently speak 5 languages and found FW impossible to read. Many experts in the field would agree that Finnegan's Wake is interesting only for linguists.
As for Ulysses, it's the masterpiece, still very difficult reading, but way easier than Finnegan's Wake. You must be really determined and very concentrated, but you will make it. It helps if you read Homer's Odyssey first, it will give you somewhat better understanding, because Ullisses actually refers to Odyssey. (Ulysses is another name for the Greek hero Odysseus.)