Don't want to play Tyranids? There's cards for you, still, in this set. Each gives you new resources against your opponents, be they Tyranid or otherwise.
From the release:
Fantasy Flight Games is proud to announce The Great Devourer, the first deluxe expansion for Warhammer 40,000: Conquest!
A new horror approaches – a ravenous species, sweeping through space and filled with an insatiable hunger. This horror is known by many names: the Great Devourer, the Doom of All Things, the Penance of the Elder Gods. To the Imperium, they are the Tyranids – biologically engineered super-predators perfectly adapted to slaughter and harvest new biomass from conquered worlds. Their numbers are legion. Their hunger is as boundless as space itself. Their only goal is to devour and destroy until the galaxy is lifeless and dead. Now, they have come to the Traxis sector.
The Great Devourer is the first deluxe expansion for Warhammer 40,000: Conquest, and it introduces a brand-new faction to the game: the Tyranids! Two Tyranids warlords lead these horrific creatures into battle, each offering a very different play style. In addition to these warlords and their signature squads, you’ll find a host of new units, supports, events, and attachments to support the Tyranids, including an entirely new type of unit, the synapse unit. The Tyranids aren’t the only ones to benefit from this expansion, however. Every other faction must make its stand against the Great Devourer in the Traxis sector, and brand-new unique characters help them to battle the Tyranid threat.