How will it become the next Halo? I'm confused. The game plays nothing like halo, the story is nowhere as deep as Halo's (let's admit it, Halo has come a long way in terms of 'lore' or whatnot), and once Halo 3 and the Halo movie comes out, people will forget about Perfect Dark. You can't put hope in having PD0 be a 'Halo-killer'. Many have tried, none have succeeded. I'm not saying Pd0 will be bad, it might be great, but that doesn't change the fact that the Halo series is, well, the Halo series.
When True crimes came out, people said "YES! This is the next GTA! You can arrest people and it has a better fighting system!", but once GTA came back into the market, "What's True crimes?"Here's something atad-it fanboyish for you.
Unless this so called "halo-killer" fps game: is exactly like halo, and much much much better (whatever that may mean), gains more buzz than Halo (this would be ultimately hard), gains more recognition (Halo is one of the most recognizeable games right now), gains more media space (halo movie, media-driven Halo tournies, halo on mtv, halo halo halo), gains more online gamer support (Halo2 drove Xbox Live's service to where it is now), has a more-kickass hero (can you beat the Master Chief in terms of military super-soldier design?), has a better story with story-support (in-depth, developed, interesting, widens the appeal of sci-fi to different audiences, action-packed, dramatic, "apocolypse-driven, humanity-saving, hero-centered" story), and so on - it will have a hard time overcoming such a beastly franchise.
It's one of the reasons why GTA is still a top-seller. Perfect Dark will not become the next Halo, take my word for it. If I am wrong, I will admit it and give you a cookie.
I'd go for PD0 over PGR3, though.