A fast, smooth adventure, with gorgeous graphics and tight controls.
The world around Samus is highly explorable, with tons of things to scan and enemies to kill. Planets can be re-visited at any time, with backtracking highly encouraged. You WILL want to track down every last missile expansion, energy cell and ship missile before the final, epic battle.
Negotiating the environment is a challenge in itself, with the grapple beam, ball mode and upgrades constantly affording you new, intriguing ways of exploring the environment. And the Wii controls are so beautifully implemented, you'll forget you're holding the Wii-mote/Nunchuk.
To summarise, Metroid Prime 3: Corruption is a large, mature, smooth FPS, with smooth controls and solid gameplay. A must-own for any self-respecting Wii owner.