I just finished reading the Silmarillion. Back in the fall I read The Lord of the Rings and in winter I read The Hobbit. I'd read all or parts of these before, but I'd never read the Silmarillion.
Tolkien's books are always slow starters - you have to read a 50-100 pages before the story really pulls you in, but after that it becomes very interesting. The Silmarillion is definitely no exception to that, but the 100 pages or so take even longer to get through because those pages are so dense with names and place names that it is hard to follow. You get names for myriad places and people, and often the same place or person has two or three different names - in Quenya, in Sindarin, in other languages as well. And then it gets hard to keep track of some of the people who are not as major in their roles as to who they are - who they are related to, what is their heritage, etc. And yes, all that information is pretty important to the stories. When you get to the end of the book, there are many pages of maps, family trees, pronunciation guide (it's "keleborn" not "seleborn"!), name dictionary, etc. And you actually read some of it because it is necessary.
The Silmarillion (as published, which includes several other tales as well such as the Akallabeth, the story of Beren and Luthien, etc.) is a mythology/history/creation collection. For anyone who has been interested in LOTR, it is really worthwhile because it provides a history of Middle Earth from the creation story up to and including the storyline of the Lord of the Rings - but the events of the Lord of the Rings are only the last few pages of the book and you get that story from a different and broader perspective (and of course in much less detail).
Now I just have to decide do I want to keeping reading and start in with the works that Tolkien's son Chris wrote in on because his father hadn't finished before he died. Anyone read any of the post JRR works and can weigh in? And where to start exactly?