As in other installments of the saga, in Metroid Nexus you have to investigate a complex labyrinth full of dangerous enemies, doors that need opening, and above all, areas that require you to level-up your hero if you want to gain access.
At the beginning of the adventure, Samus can only jump normally and use a basic shot from her weapon. However, as you progress through the game, you can improve and expand her abilities. You can convert into a ball to roll through narrow areas, or use a charged shot, just to name a couple examples.
Metroid Nexus is a fan-made game with some ambitious goals (various different zones, up to five final bosses). It also includes good graphics and audio, and really wouldn't be out of place next to the Super Metroid games.