Great stuff Paul, glad to hear it. I would hate to think we steered you wrong, though recommending Metroid Prime is a pretty sure thing except for the biggest sticklers out there ;). And if you're only 11% through the game, well, I can safely say that the best is still yet to come :).
Metroid Prime is one of those games that I'd have no trouble recommending to anybody, myself. I have a friend who is a female teacher who can't play anything more complicated than Mario Sunshine and she was playing it non-stop. For a first-person exploration game to hook people like that is...
What're my choices again? I can't read the small print :D. I haven't played Splinter Cell, Paul, but I can tell you that Metroid Prime is one of the best games I bought for my GameCube and I loved every minute I spent playing it. It takes a bit to get used to the controls, but it's way fun...