Realistically, I don't think anything can really kill the haughty Halo hype machine. But if anything can do it, it will be Unreal Tournament III.
Before someone flies off the handle, let me clarify that yes, I have played the original Halo, at my cousin's place a while ago and played the PC demo. It did nothing for me. It felt slow, vehicles tended to float unrealistically, and it overall didn't feel like a run and gun game, more like a walk around and maybe shoot something.
Overall, it felt restricting.
Granted, I was more used to the six degrees of freedom granted by Descent 3, but even understanding that Halo involves a person on the ground and not a zero-gravity spaceship in tunnels, it still seemed lacking.
In early 2006, tired of flight sims and sporting a new GeForce 7800GS, I downloaded the Unreal Tournament 2004 demo from nVidia's nZone page.
I was blown away.
Everything was smooth, the weapons were amazing, and above all, it was fast! The idea that standing still got you killed made sense!
With rejuvinated in the first person shooter genre, I purchased it the Editor's Choice Edition, only to be further amazed by it's brilliant AI, extensive mod community, and wonderful vehicles. And I have still yet to really crank the difficulty!
Over time, I had determined (based on pure conjecture) that someone who had played nothing but Halo wouldn't last five minutes of Unreal. I developed the notion that any FPS fan worth his salt would recognize Unreal's superiority. I even began to proclaim "Halo is for wimps, Gears of War is for cowards (with it's duck and cover system), Unreal is the champion of shooters."
Now, I have played the Unreal Tournament III demo, and I am still aghast. Perhaps enjoying the Battlefield 2142 community has made my Unreal skills rusty, but I doubt it. I find it more likely that Epic has succeeded once again.
And now, let us all revel in Epic's accomplishment.