I hope you developers play around more with futuristic-aesthetic materials. The iridescence effects painted into Halo: CE’s cubemaps aren’t only unique to Halo:CE, but their vibrance appears unique within the Halo series. Before reflection models were actually mathematically evaluated per-fragment in video games (Phong shading), I think specularity appeared much more beautiful, natural and creative than it did when Phong shading was introduced to games. Only now are we developing material systems and lighting models sophisticated enough to compete with the albeit analytically flawed reflection mapping techniques of 1997-2005.
Good on Keith and Jan for paying a lot of attention to this!
Before Halo:CE, the futuristic materials were even more prominent (less Covenant purple and UNSC grunge) 
At least the Warthog windshields were still pretty sexy in Combat Evolved.
Sources:
http://halo.bungie.org/screenshots/bungie2.html
http://halo.bungie.org/screenshots/bungie1.html
http://halo.bungie.org/conceptart/