Metroid Prime 2: Echoes

The sequel pushes the concept into a world split between a light and a dark dimension, between which Samus switches to solve ingenious puzzles. Echoes is noticeably harder and more demanding than the first game, with more aggressive enemies and a darker atmosphere. It also adds multiplayer, though that is more of an add-on. For fans of the original, it is a great, if at times merciless, adventure that spares no challenges and rewards patient explorers.