Hm, I think level design has a lot to do with this topic - as its part of the "art" factor.
I never played the first Halo, but based on spike's statement, I'd say he wasnt talking about the level's design in relation to the gameplay, but only in visual terms. So I guess he did never experience the levels viual design as outstanding or stunning.
Referring to darkinfernos last statement, I also dont think there's just stylized and photorealism - just take a look at Mirror's Edge, it is without a doubt very stylized, optically speaking, but in a technical way closer to photorealism than, say, Half Life 2.