Well, I think it's some of this 'n' some of that. No doubt that many a discerning gamer will prefer
CoD4 for perfectly legitimate and easily understood reasons, while a lot of its success has to do with mainstreamers immersing themselves in a more, well, 'mainstream' scenario (modern war). This could be anyone from my intelligent friend who has a borderline allergic reaction towards anything vaguely sci-fi (although he did love
Halo 3, probably because he got it free and because it's still strongly tied in to our planet and traditional 'epic war film' set pieces), to the "Git-R-Done" crowd that really wants to experience their ultimate 21st-century fantasy of clearing out Middle-Eastern towns on their own. There's also the element of The Contrarian Gamer, who has been picking on the
Halo franchise for quite some time now, and champions whatever its most direct competition is.
Me, I think this isn't very surprising news at all, as Master Chief's pop culture arch has got to be on the way down, now. Three games, six-plus years of hysteria...people just move on organically. Sometimes this is gradual, sometimes it's virtually overnight. Watch the same thing happen with
GTA IV.
EDIT: I'd also like to add that another factor is simply the
Halo Xbox Live experience becoming synonymous with "insufferable a-holes", for a greater population than just the "gaming crowd". It's the 'poster boy' for everything that's bad about playing games with strangers online, and this creates a self-fulfilling prophecy, or at the very least, severely diminishes the amount of relatively civil and mature people from even setting foot into its arenas. It also stands to reason that 'the kids' won't abandon it for a very long time, as it's much easier to jump in and
around in than so many other shooters on Live right now. And no, I don't think
UT III will draw these brats away
en masse.