People expect every new game to look 10x better than its predecessor, or else you see these posts like "it looks like ass" or "so 2005!" or "consolized!"
Incorrect. WoW sells like hotcakes and it has shitty graphics. Orange Box has decent graphics and it sold like hotcakes. Crysis had the best graphics and it sold like warmcakes. UT3 had great graphics and it sold like fruitcake.
And CoD4 was hardly an exception to any rule. Its single-player campaign was 5 hours long. Its level design consisted of throwing endless hordes of stupid enemies at you until you found the trigger to turn them off. CoD4 epitomizes great presentation, outdated gameplay.
If anything, I think the underwhelming sales of Crysis and UT3 have proven that PC gamers care more about gameplay than graphics.