Enter the World
Why it is hard sci-fi
Soft sci-fi by the sites own measure. The science is decorative and unobtanium is a fig leaf. What earns it a place is the worldbuilding logic. Pandora orbits a gas giant in the Alpha Centauri system. The atmosphere is unbreathable for humans. The Na vi biology, neural plug interfaces, and ecology of the moon are internally consistent across the films.
Science inside it
Tidal locking and eclipses around a gas giant, exotic atmosphere chemistry, neural interfacing through a wired biological connection that links every organism on the moon. The avatar driver model is a remote teleoperation problem with a real lightspeed delay if you took it literally, which the films do not.