7th Edition was the last version to use physical plastic templates for explosions and flamers, a mechanic many purists miss.
Many factions received dedicated 7th Edition books, while others continued using their late 6th Edition books (which remained fully compatible). Warhammer 40k 7th Edition Codex Pdf
One of the final major additions to the edition, bringing a unique "Ambush" mechanic. 7th Edition was the last version to use