If you think Ulysses is tough, try Finnegan's Wake, which is utterly unreadable.
I don't know whether or not I would agree on that personally... I've not yet tackled
Finnegan's Wake, though I keep meaning to. I do know some people who have read it, though... some of which abhor the thing, others love it. From what excerpts I have read, as well as what I understand, one has to really soak in that book, with its various levels of wordplay, intertextual reference, shifts in voice and mode, etc.
Personally, this is the sort of thing I can sink my teeth into and relish; but I must also have a fair amount of time to devote to it in order to get the full benefit of it, and that is something I seldom have for the time being. Also, I want to get a truly authoritative edition, as close to Joyce's intent as possible, as both this and
Ulysses have an intensely meticulous use of the language and technique, and editorial, typographical, and assorted other alterations can make a profound difference in the reading of such a book....
I would say that, if you are able to read and enjoy Aldiss'
Barefoot in the Head, you have a fair chance of enjoying
Ulysses and, most likely,
Finnegan's Wake....