Metroid: Samus Returns is a exploration-based sci-fi/action game in which Samus has been sent to destroy the Metroids. The game itself is a re-imagining of the 1992 Game Boy game, Metroid 2: Return of Samus.
Though it's been tweaked a little since the original, it still has the same charm as the original game. As pointed out, the game looks gorgeous on the 3DS with a lot of background detail to make the whole thing pop off the screen, especially with the 3D feature turned on.
Samus now has full motion to aim as opposed to the original's 45-degree angle, which makes combat more precise. Samus also has new abilities to compliment the difficulty of the game on the whole.