The first - and most of each of the last two - chapters are system agnostic but there are plenty of ideas throughout that could be grafted onto other systems with very little effort. I think it's one of WotC's better 3e era books. It compares favourably with the Races Of… titles.
The opening chapter, a summary of drow culture, is far more in-depth than anything you'll have encountered in a Races Of… book. Those tended to feature three races per book, whereas here, the whole volume is devoted to drow (and it's twenty-nine pages longer than Races of Destiny, for example). The descriptions of how drow society and its its institutions function are coherent and reasonably believable (think Game of Thrones machinations on steroids).
Chapter two is about drow options, and they are plentiful. There's a brief discussion of putting a drow-centric spin on some skills (bluff, craft, handle animal and speak language), before the chapter launches into a rich variety of new feats (including ambush feats, divine feats, weapon style feats and divine feats). These are complemented by sections on new class features, new spells and new invocations. This chapter alone makes the book worth it for anyone who wants to feature drow heavily in his 3e campaign and it offers lots of ideas to 5e players.
Chapter three is all about new prestige classes, inevitably. Now, I don't do prestige classes, at all, ever, so I simply cannot comment on this chapter, because frankly, I skipped it. But it's there.
I love it when books feature new equipment, because introducing new gear to your game is one of the easiest things you can do, as it's easy to limit the availability and reliability of exotic devices. Having said that, one of the first devices described in chapter four (the spider kit) is pretty draft. But other items make up for it and there are sections on alchemical items, poisons and magic-infused poisons, weapons, new weapon properties, armour and shield properties, clothing, tools and artifacts. It's a drow DM's bazar, again easy to adapt to 5e.
Next there's a chapter on monsters, the best of which is an albino form of drow (that can mingle undetected with its surface-dwelling counterparts). The Kuo-toa gets another look, with expanded stats for whips and monitors and a section on kuo-toa lore). But while this this chapter inevitably revisits these things and anything arachnid, it doesn't have anything worth shouting about. The monster entries do come with sample encounters, though, which are welcome and will be put to use one day. But that's me thinking 3e. There is perhaps less value in this for a 5e player, though the creatures at least provide conversion starting points.
Chapter six deals with campaigns. There's guidance for DMs on how to set about creating or incorporating a drow theme for your game. Then there are descriptions of the drow environment, drow settelements, underdark flora and fauna and natural hazards. After that is a handy (for 3e DMs) section of ready-made drow NPCs (who range from the individual to frequently encountered types, such as priestesses, slavers, wizards, assassins and favoured consorts). Unfortunately, the closing section of this chapter lets the rest of it down. Called 'drow adventures', it's a set of encounters tied to those utterly awful DDM maps that starting appearing in the mid- to late-3e period. The maps are awful, because they were designed for DDM skirmish games, not exploratory RPG play. The encounters section isn't a total write-off but I'd recommend re-keying the listed encounters to much better maps, for the sake of your game. This section is the least value of any to a 5e DM.
Like chapter six, chapter seven doesn't quite fire on all cylinders. It's a guide to the drow city of Erelhei-Cinlu. After an overview, all the major drow houses are described. There's essential guidance on the treatment of outsiders, and descriptions of sights and sounds, each of the great city's wall sections and major regions (called ghettos). This is all pretty good. Unfortunately, however, instead of some handy encounter tables sprinkled with a few imaginative and colourful example encounters, there's what is in effect a reprise of the end of chapter six, with more martial encounters using those DDM skirmish maps. What this book's encounter sections lack in variety, they certainly seem to try to make up for in number. To be fair, much of what I found tedious about this section is down to its expanded treatment of the Ceremonial (i.e. gladiatorial) Arena and the inevitable tournament combat options for PCs. If this is of potential interest to your group, this section is a bonus. The latter part of the chapter has ideas that may be of interest to the 5e DM but it's mostly 3e combat-based.
Finally, there's an appendix aimed at PCs. It starts by discussing drow as foe and, curiously, gives PCs tips on countering typical drow strategy, which would seem to be stepping on the DM's toes a little (as in, raising players' expectations of drow opponents being played tactically a particular way). This section of the chapter would be of greatest use to a 5e DM. The second half of the appendix is about playing drow PCs but much of it is in the form of rules for 3e. These include the inevitable, box-ticking Drow Legacy and Half Drow feats, before concluding with the potentially more useful twenty level drow racial class, a Savage Species-like treatment that enables players to begin playing drow at first level while having an ECL of 1, picking up the complete set of standard drow abilities over three levels. I can't imagine many players wanting to stick with the class for another seventeen levels, myself, but they're there for those who want them.
