Many people I know don't like the high style because it's not everyday speech, which makes it a bit of a slog to read. I rather like it, though. I've read LOTR, The Hobbit, Silmarillion and The Children of Hurin, and really, I can't get enough.
The stories are so layered and the plots are so complex and intertwined that, when you've finished the Silm and go read The Hobbit or LOTR, you find it's a different experience because you know more about where the Elven and Men characters are coming from.
I love the Silm because its themes of jealousy, sex, death and betrayal have consequences that trickle down through the ages. That, and the snippets of "history" that make you wonder more about what happened, why and when in the gaps between "recorded" events.