The breaks in the sections and specifically the upper deck make for a much less intimidating feel.
Shea, old Yankee stadium, and other old stadiums were much more intimidating to the opposition because it was literally like a sea of people throughout the entire upper deck.
Also, the sections were steeper and the rows were much more on-top-of-each-other/cascading, making for much louder stadiums.
That is all.
I've been to Citifield at full capacity and at its absolute loudest. I was at the first game when Wright hit the HR vs. the Padres to tie it and the place exploded...I doubt it was ever louder in the building than at that point, based on the way Mets baseball has gone in Citifield. It was definitely pretty loud.
But it was noticeably less loud than Shea at its loudest (I was there for Pratt's walkoff HR, Wright walkoff off Mariano, among others).
I am not one of your relatives -------------------
I know you aren't because all my relatives are intelligent. Even those still in the sixth grade thought that your name calling was silly.