As with the other Codices for the tenth edition of Warhammer 40,000, this version of Codex: Necrons includes all the rules and lore that players need to use the faction on the tabletop.
The background section of the book appears to be a mix of reprinted and newly written lore (most of the important dynasties getting a few extra paragraphs added to their description compared to the last Codex for example). The three short stories included in the lore section of the book were all quite good, with my favourite being the one about Anrakyr the Traveller as it gives a good idea of how he operates, and it is also good to see he hasn’t been forgotten despite not having rules this edition outside the downloadable Legacy rules.
The rules are pretty standard for tenth edition, simplified and less diverse compared to the previous version but seem reasonable. As well as the basic Datasheets, the book also, of course, includes rules for the Combat Patrol and Narrative styles of play, with the Narrative rules focusing on waking a Tomb World rather than last editions mission earn Dynastic Epithets for characters, which seems quite interesting.