Eberron

All in all, it's a nice complement to the Eberron Campaign Setting.

There isn't much repeat between the two products, but rather they complement each other by either providing more flavour or more details to what was already mentioned in the campaign setting.

The interesting thing about this sourcebook is that its topics are organised alphabetically - a novelty among D&D sourcebooks (excluding monster manuals of course). It's not all lore, flavour text, and adventure hooks. Interspersed throughout the entries are a few feats, spells, prestige classes, special items or materials, and psionic powers. Nothing really outstanding, but they help flesh things out.

What I did like are the sidebars that attempt to incorporate the non-setting-specific materials found in other sourcebooks into the Eberron setting - things like other races and classes, and even special terrain elements. They may seem like ads, but I found them a nice touch.