While this article only gives passing mention to Halo itself, The Gaming Intelligence Agency does talk a bit about the splash the Xbox made at E3-- to the effect that it wasn't as much as, say, Nintendo's GameCube. YMMV.

But the interesting part, aside from their comments on the Xbox controller, was their assertion that they saw an Xbox crash-- yes, crash-- during a demonstration.

There were also indications that the hardware is not entirely stable yet - a crash during Nightcaster revealed a familiar looking PC boot screen, and a Microsoft representative explained that the memory configuration on the floor models was different than that of the final version.

Apparently Microsoft is saving all the non-crashing RAM for the models they intend to sell. But at any rate, consoles aren't supposed to do this-- especially not ones that have supposedly had their designs frozen. However, as far as we understand, the machines on display at E3 were actually XDKs and not release-spec Xboxes, so that might go a long way towards explaining what happened.