I recommend reading a couple pages [1] to get a feeling for Finnegans Wake - it's amazing the density of concepts Joyce crams into words, with multiple meanings in almost every word. I kept thinking the book would make more sense if I kept reading, but no, it's like this the whole way through. A few things get better, for instance, the initials HCE constantly appear, so in the first sentence you should get an aha feeling from "Howth Castle and Environs". But that's a pretty small payoff.
If you enjoyed the book and found it hilarious, more power to you. But as someone who likes challenging books and put a lot of time into Finnegans Wake, the book didn't do it for me.
[1] Finnegans Wake is online at http://finwake.com/1024chapter1/1024finn1.htm along with detailed notes, but unlike Shakespeare, looking up mystery words doesn't make things any clearer.