My impressions at the halfway point:
I'm actually in the middle of reading this right now (I've just finished the Nausicaa episode to be exact). So far, so good. I'm enjoying it very much, but only because I'm cheating. I'm reading with the help of the book The New Bloomsday Book: A Guide Through Ulysses by Harry Blamires. I went to the library to see if I could borrow an annotated edition of _Ulysses_ but they didn't have one so I borrowed this book instead. A great paraphrase which elucidates most of the allusions and cross-references, without trying to interpret the book for the reader. I'd highly recommend it.
I'm not done yet, but I can tell you, it's definitely worth the read.
And when I was done (I was just about speechless, LOL):
What a great book! Challenging, sure but absolutely wonderful. I admit I did find parts of it a little slow and other parts difficult, but over all I really enjoyed it. A masterpiece. I loved it. I felt like kissing James Joyce when I was done.