The basis of the game is that you are a secret CIA agent named Sam Fisher who must sneak around various bases to recover information for the American government. This is the first of the series and it's stealth gameplay is very popular. You control Sam from a third person perspective and must sneak through shadows, take out guards silently and use gadgets to progress through levels. Don't worry if this sounds complex because there is a detailed training mission, although you will always find it difficult and sometimes numerous attempts at missions and hiding in shadows is necessary.
The graphics are some of the best on the gamecube and help to immerse you in the experience because they are so smooth and detailed, particularly the use of light and shadow which is vital for sneaking around levels. I became very frustrated at times because of having to repeat levels after being seen but I did persist and I found that when you do it is generally worth it. You should be aware there is no multiplayer but there is in some later games of theseries so if that is an issue they might be worth considering.