Read in Italian and found absolutely boring and obscure when I was 10 years old and just done with the Lord of the Rings (and already knowing by heart the first 20 minutes of the Ralph Bakshi's cartoon).
Re-read in English on November 2011 after having found a wonderfully preserved first edition for just 4 £ in a charity shop. To put it as straight as I can, The Silmarillion is the Bible of Tolkien's mythology and cosmogony. This means that you cannot expect any humour or brilliant dialogues here, but a heavy old-fashioned narration of the events of the so called First Age of bygone Beleriand where Elves dwelled and which used to stand at the north-west of Middle-Earth before being swallowed by the sea.
If you're not into Tolkien's world, just leave it: you won't find anything that you may like here. This is a book for Tolkien's geeks who not only know what Numenor was but where to put the accent on it. Let's face it: The Silmarillion is an extremely accurate imitation of a whole mythology. Here Mr Tolkien didn't care about details and made an apparent mess with first names (among the ones who belong to several characters on different ages we have Glorfindel, Denethor, Boromir, Gothmog).
Still, as a half-geek for all that concerns what Tolkien invented, I enjoyed this book at this time and spent more time than necessary looking at the map of Beleriand attached. And yet, I do think that this book could be a burden if not a bane for all those who became familiar with the Lord of the Rings thanks to the entertaining pop movies directed by Peter Jackson.