As with every Sine Nomine product, Worlds Without Number focuses overwhelmingly on the person at the session who needs the most support: the Gamemaster. If you embrace its myriad tables, you'll make worlds, adventures, NPCs, and monsters that surprise you, shaking you out of your well-worn habits.
On the player side, you get mix-and-match classes to build a variety of concepts, as well as item crafting, domain management, and long-term project rules that encourage proactivity and ambition. Any game can tell a story about heroes who change the world, but not all of them lay such a clear, enticing trail of systems that empower that sort of play.
The Deluxe Edition adds six extra partial classes (Edit: Five partial and one full class) for more concepts, heroic rules for amped up PCs, and the Legate rules that supercharge your party with a wink-and-nod to fans of Godbound. There are some additional GM tools there too, a few of which give you neat ways to twist or question your content to extract new insights.
Enthusiastically recommended. The free version is more than enough if you're skeptical or price sensitive, and allows every player to have a personal rules reference. But don't sleep on the Deluxe Edition if you like what you see.