This is a sourcebook describing a variant version of the standard d20 elf. (I'm not sure where the title comes from, incidentally, as they are never referred to as "moon elves" in the book, and they don't seem to have any obvious lunar connection). The intention, however, isn't for a minor race of elves in some obscure place, but as a replacement for the standard version - although there wouldn't be anything to stop you using it as the former, of course.
For the most part, these elves do follow the usual tropes, and they are instantly recognisable as elves - there's nothing dramatically weird or different here. However, there are changes to the usual version here and there. For example, they tend to be more lawful in nature, and they age at a different rate to the d20 default. So it's a distinct vision, but not a radical re-imagining.
Around a third of the book is taken up with a very detailed account of elven society, that covers just about anything you'd want to know concerning any culture. This really comes alive (although its not going to be very relevant to a dungeon-focussed campaign), and is both well thought out and thorough. It is accompanied by excerpts from the diary of a human compelled to live among elven society, that's rather better than most such fiction, and complements, rather than distracting from, the main text.
The next section covers elven items, both magical and mundane. There are a range of clothes described here, many of which are for flavour, rather than providing specific rules effects. Others, however, range from providing minor bonuses up to 5th level magical items. This is followed by some potions and a host of magical items of various kinds. Most are low to moderate level, but with some that are much higher. In general, there isn't a strong elven feel to them, beyond the descriptions, but they are fitted into the culture outlined in the first section.
The weapons and armour are rather more obviously elven, and there's a great section on magical arrows, with a number of examples. That's followed by even more magical items, presenting a wide range of different powers; many of these have a 'nature' theme, although the actual effects are quite broadly applicable. There are three unique magical artefacts (although one's essentially a joke) and three cursed items - something one rarely sees in these sorts of supplements.
The third section of the book deals with magic. There are many spells here, most of them between first and third level, although with a few stretching all the way up to ninth. Rangers and druids are best served here, since many spells have a natural theme, but there are also a number of sorcerer/wizard spells, related primarily to stealth and grace. There are ten clerical domains included, based around elven themes such as nature and beauty. On the whole, these are going to be more useful in wilderness or social/city based campaigns than down a typical dungeon. Some of the granted powers might even be a little overpowered for the latter.
The fourth and final chapter provides prestige classes. Presumably, they're intended only for elves, although, technically, the class requirements don't mention this. Foresters are a way for rangers and druids to specialise in stealth and sneak attacks, although they don't really provide anything else. The carouser is a party animal who specialises in social skills such as Diplomacy and Bluff, and therefore is obviously only going to work in certain campaigns. Nor is there any particular reason why they should be restricted to elves that I can see.
Noble warriors are more obviously combat oriented, but giving a mix of social and leadership abilities. Rather more directly useful in a fight are the sword-singers, with abilities related to rapid movement and enhanced damage. Similarly, rune-blades are warriors with some magical abilities bound into their swords - there are a range of different options for this one.
Spotters specialise in, well, Spot checks, with a few other vision-oriented abilities thrown again. Which can doubtless be useful, but is probably rather narrowly focussed for most tastes. Finally, there are masters-of-tongues, with abilities relating to subterfuge and infiltration; some of these are combat related, although they're probably more useful in an urban setting than elsewhere.
Most of the interior artwork is reasonable, although no more than that, but the cover, and the pictures used for the prestige classes are rather better. On the whole, the book is well written, and well laid out, although there's a fair bit of colour that may be a problem if you're intending to print it all out. At over 100 pages, it's also quite a hefty tome, and very good value for the price, causing me to nudge it up into the 5-star bracket.
If there's a downside, it's that this is not so useful for traditional D&D style games. To my mind, that's not a bad thing; this book, like the elves it described, focusses on social interaction and on agility and perception rather than brute force. Some of it, at least, is therefore going to be useful in any campaign with those themes, whether or not elves are a major focus. But it's probably wise to be aware of that.