What a great game..
Basically the game's a mixture between jump & run - adventure exploring and first person shooter. After you passed the in-game tutorial you land on a foreign planet with all your equipment spread somewhere in the levels. Of course your quest is to find the equipment and save the planet. Therefore you will encounter various ennemies to regain your belongings. Along the way you will also find health packs which permanently increase your max health and so on. And When you find a new weapon you get access to new areas of the huge levels so the game includes some backtracking but due to the nicely decorated ambience and many different ways to get to your target the game never gets boring. Additionaly you often must search for additional hidden objects (like rocket bags that increase your maximal amount of rockets) which is necessary to defeat the next boss.
After defeating the final boss many palyers (including myself) continued to search for the remaining hidden objects, so the game will keep you busy even longer. You can even play the game again but with tougher adversaries to make the game more challenging.
All in all the game is a must for all gamecube fans.