The Children of Húrin (pronounced HOO-rin) is one of J.R.R. Tolkien's posthumously published books (edited by his son and literary heir, Christopher Tolkien). I won't go into great detail about where, when and how it fits into The Lord of the Rings, mostly because I'll get it all wrong but also because it does and doesn't fit.
If you're a Rings fan, it's hard to say if you'll like it. I would recommend it just because it's Tolkien but it certainly adds to the richness of the world that he created. The characters (Frodo, Bilbo, Gandalf, Gimli, etc.) are not present, the story is much too early/old for that. If you're not a Rings fan, I'd still recommend it. It's a neat story. At times you might think you're waiting for Beowulf to show up. In some ways, it is written in much the same way (excluding the lyrical poetry).
There are several pages of family trees that are quite helpful (in the back). They're not advertised and so if those things matter to you, go read them first. Only a couple of names will be familiar to you so if that sort of thing matters to you, go find and read them. They help in placing the story in its proper context.
I found the first few chapters someway pedantic since we get an overview of how we got to where Tolkien wants us to be. After the plot gets going, though, it was quite difficult to set down. Something of a cross between a history and a tragedy, I felt sorrow with and for the character and his family on a number of occasions.
There are a number of drawings by Alan Lee and they add to the book rather than detract. They're not Tolkien's line art, but they are pleasing.
I don't think it sold very well; Border's frequently has it on sale for 30% off and here's a coupon (that always seems to be refreshed/current).
