Free Aim

Free Aim or Free Aim Mode is a new feature in Metroid: Samus Returns. Previously, in 2-D Metroid games it was only possible to aim diagonally, horizontally and vertically. Free Aim now allows Samus to aim at 360° to more precisely target enemies. To further assist with shooting, a laser sight has been added to Samus' Arm Cannon; it will glow red when it intersects with an enemy.

E3 website
"Classic Metroid II: Return of Samus gameplay is joined by a wealth of new content, including a set of brand new abilities that utilizes a mysterious energy resource called “Aeion,” a powerful melee counterattack, and 360-degree Free Aim Mode."

On-screen tutorials

 * "Press and hold [L] to lock your position and enter Free Aim mode."
 * "Use [Circle Pad] to aim in the direction you wish to fire beams and missiles."