Perfect dark isn't a copy, it just uses the same game engine from the same developers. Thats like saying Heretic and Soldier of Fortune are the same game, or like saying Rainbow Six 3 and XIII are the same game. Infact, two years before the release of Perfect Dark most of Rare had quit to form Free Radical, and it was basically a brand new team working on Perfect Dark. You could tell some of the textures were recycled, and some of the music was remixed from GE, but the story was 110% origional.

When it comes down to multiplayer, GE is obviously more fun, but as far as single player is concerned, its a pretty tough decision. For being release three years earlier and being just as fun, I'd have to give the advantage to GE, but PD introduced co-op and counter-op. I'm not sure if any of you guys ever had the chance of playing co-op PD, but it was one of the best single player gaming experiences I've ever had.