This review will contain spoilers!
In many sentences:
On the whole this was an enjoyable collection, with the first half being particularly good. The three short stories ("Smith of Wooton Major", "Farmer Giles of Ham", and "Leaf by Niggle") were definitely the highlights for me. All three had that peculiar quality and style of a story by Tolkien, and I found myself completely enthralled in all three. I don't remember having an complaints about any of them.
One thing that did really surprise me about this collection, however, was the essay "On Fairy-Stories". After enjoying the many literary essays I've been reading by C.S. Lewis lately, I assumed I would love reading one by Tolkien. Surprisingly, though, the essay felt disjointed, unclear, and generally hard to follow. Reading an essay with these elements isn't that uncommon, but considering it was written by Tolkien, whose fiction has always struck me as extremely well-organized and logical, this was shocking. This isn't to say it was bad (on the contrary, it is full of fascinating ideas, especially in regards to the idea of sub creation), but it was a letdown compared to Lewis' literary works. I think it would improve on a second reading, but that will have to wait for the time being.
I'm not a huge fan of poetry (probably due to my own failing) so the Adventures of Tom Bombadil was not very exciting. I found myself glossing over most of this section. This should not count against them, however, but rather against me and my inability to appreciate poetry. "Sir Gawain" was better, but probably because I ended up treating it more like a regular story than any sort of poetry. I'll even admit that I didn't catch the alliteration on each line for about the first 25 stanzas. Embarrassing, I know. What might be even more embarrassing is that I didn't even give "Pearl" or "Sir Orfeo" a chance. I simply put the book down, having had enough poetry for now.
I think the short stories are for anyone, fan of Tolkien or not. The essay, unlike Lewis' essays on science fiction, however, should really just be read by people who love fantasy and want to understand some of its history and literary merit. As for the poetry - I'll leave that for someone better able to discuss it.