Nobody is calling it a Halo killer any more. To be frank, most PS3 fans couldn't care less about Halo. Nobody is calling it a Gears of War killer, either.
I would have been disappointed if it was worse than Halo 3, but it'll never reach 9 million sales. It's definitely on par with Gears in terms of quality, but again, will likely not get the sales. It has a shot at Gears 1 sales, but it's not a certainty or even likely, really.
In case anybody thought I didn't like KZ2 from that post, look at my avatar...