Expansion packs

What you're actually buying

A new campaign, units, classes or content for a game that was already complete, sold separately at roughly two-thirds of the original's price. The base game still works without it. You see what's in the box before you pay.

How it works

A hit game's engine and art were expensive to build and cheap to reuse, while retail shelves rewarded a steady drip of new boxes. The expansion pack solved both problems. Players paid once, up front, for content they could see on the shelf, and there was no subscription, no ongoing online service and nothing metered. On PC there was no console platform royalty to pay either. Expansions let franchises feed themselves between sequels, and matured into annual content machines such as The Sims.

When it's fine

When what you get is clearly new content and the base game stays complete without it. It is the last fully honest version of an instinct that later turned into DLC.

Where it came from

StarCraft: Brood War (December 1998) added new units and a full second campaign to a game already out for a year; the two sold almost 10 million copies together by 2007. Diablo II: Lord of Destruction (June 2001, $29.99) shipped over 2 million units within a month, which Blizzard called the fastest-selling PC expansion in history at the time. Even a mission pack built by another studio could sell well: Gearbox's Half-Life: Opposing Force shipped over 1.1 million retail copies. The Sims (2000) became the best-selling PC game in history by March 2002 and spun out seven expansion packs for the original game alone. The model eventually dissolved into the always-connected internet, where the same economics resurfaced as paid DLC and then microtransactions.

Historical prices and revenues are in US dollars at the time unless marked A$.