[Suzerain of Sheol]

Yeah, I'd so. The other books all build off of the Silmarillion, but they're even less coherent. In the form it's published in (which was arranged by Christopher; who knows what J.R.R. intended) the Silm. is at least a more or less complete story, even if it skips huge chunks of time and flips between dozens of different characters.

It's not an easy read by any means, but I found it really rewarding once I got a grasp of what was going on and who was who. And weirdly, while it's really light on character development, some of the stories are a lot more emotional and hard-hitting than anything in LotR. It's also a lot less black and white than LotR is, in terms of morality.