I have this game for the PS2, and have played it for the Gamecube. For starters, one shouldn't believe the claptrap that one version is better than another. That just isn't true - the GC graphics are EXACTLY the same as the PS2 one. Between gorgeous outdoor graphics of plants, wildlife and full interaction with them, cool enemies, and the BEST guns you've ever seen in a FPS, this is a title to not miss for any FPS fan. So definitely get it. Unlike most FPS, there are no maze-like structures, which is a good thing, and most levels can be understood with enough patience. For the odd level that you can't make your way out of, I'm sure there are some walkthroughs online that will be glad to help:) Not to say that it's perfect - the dead monsters disappear after a few seconds, unlike PS1's Quake 2, and there aren't as many dinosaurs to kill as there should be. Plus, 27 out of 30 levels are beautifully designed, with backgrounds and environments that will blow one's eyes away, but 3 of them (the sewers and inside the juggernaut) are annoying. But overall, it's 9.5 out of 10. Just too bad this game wasn't successful enough to warrant a sequel. But that just means it's cheaper now to be bought.
So what are you waiting for?