It's written in a completely different style... The Hobbit and LOTR are up-close and detailed stories of tiny pieces of the vast realm he created, while The Silmarillion is the exact opposite, a Cole's Notes summary of a long history with only brief snippets focusing on the individuals and their specific deeds. There are a few parts where it does delve into specific events in greater detail, like the story of Beren and Luthien, but most of it is very terse.
I found the Silmarillion as appealing as a history text book and never got past the first couple chapters. I am sure there is lots of material to build a story out off just like there is a lot of good historical dramas based on real history. I am looking forward to see what Amazon does with it.
Aside: I got in a argument with someone who insisted that Atlantis was a real place and rejected my explanation that it was fictional construct for an ancient Greek story. I wonder if there will be people in 1000 years insisting the middle earth was real?