They focus on details to explain why they liked it but they don't see the big picture: the overall aesthetics.

For example, after many dark dirty firey slimey enclosed encounters, e.g. in Naxxramas, here comes Ulduar with a spectacular transparent shiney theme, open spaces, and even some dark portions underneath for not going monotonous. [It is also the timing, the right time to release it after another instance]

It's not so much the work they put on, but often it is the theme, the idea, even if the work is a lot. It is clear that excluding some monstrous examples of haste work such as ToC, most instances have been worked on.