- It starts with a description of the city of Vornheim; places, the setting, people, superstitions. I haven't used this much at all. Why not? It's flavorful, wonderfully weird and also useful. I'm afraid I haven't used this section, because it's in the front and I've used the back of the book so much I forgot how good the front section was (serious though, I really need to set up some superstitions for my own cities).
This part is good and has a lot of good ideas, could be a bit too weird for some people.
- Next part are the three (urban) dungeons. I haven't use these yet. So, I can't say too much about it. However, even if you won't run these dungeon, they still have very useful and nifty stuff you can cannibalise in your own dungeon. The library feels the most like a classic dungeon with a lot of secrets, I feel the zoo itself is the least interesting, however every inhabitant of the zoo is interesting, so that says something.
- The urbancrawl rules are extremely useful. They are rules for when your pc's want to go from point A to C and are easy to set up during play. This section also includes a quick way to generate floorplans. I have used the floorplan generator more during play, but the crawl rules are still very useful when you need them (I just need them less).
- Next up; optional rules and tools for the law, contacts, chases, item costs, libraries and the metagame of God's Chess. Of all these I've used the library rule quite extensively and the other rules zero to three times. I usely know the costs of items player want to buy and a chase never came up, however a chase is almost inevitable to come up and there will come a day I will not know the price of an obscure item and can't be arsed to look it up. On that day I will know how to quickly resolve this situation.
- Then my favorite and most used part; the tables. It has tables for aristocrats (including quirks, character traits and relationships. Quite extensive.), city npc's (names, professions and character traits), shopkeepers and contacts, what contacts knows, getting lost/directions, a diagram for connecting npc's, encounters, fortunes, what's on the body, legal situations, magic effects, taverns and their games (my players love the games) and buildings.
Those are shit load of tables. And you know what? Everything on those tables is interesting and/or useful. You might not use one or two tables in those list, but this section has incredible worth during play.
- The front and back cover function as roll-on-tables for creatures, locations and attacks. I used these once, they're cool and innovative but they're also hidden by the sleeve. I think they are of more use to a DM who uses an old school system than one who uses a newer system*.
Vornheim is a very concentrated book. It has 64 pages, and every page has several useful things and ideas in it. It's more a toolset than a setting and with the tools it provides you can make a city that feels incredibly alive. It's one of the few books I always carry with me when I go dm'ing and in most of the cases end up using.
I would recommend trying to get a physical copy for the roll-on-tables (and, hey, I'm a fan of physical things), but if that's not possible, get the pdf, it's worth it. Every group will have at least a few adventures in a city and that's where you need this book.
*That reminds me, Vornheim is written for Lamentations of the Flame Princess, but is very much a system neutral book.