Metroid is one of the few Nintendo franchises focused on hardcore gamers. A story in space involving aliens known as Metroids that absorb energy from living beings, space pirates looking to weaponize the Metroids, and a single bounty hunter burdened with the task of eradicating both sides definitely strays from the company's family-friendly norm.
The previous-generation Metroid Prime trilogy focused strictly on first-person shooting and was a different take on the franchise's story. Metroid: Other M (on the Wii system) takes a gamble by returning to the original continuity and a third-person action style. It pays off big, though, with fantastic high-speed combat and a deeper perspective on the Metroid universe.