I think there are several reasons why the atmosphere is/was not as good as expected by some.
In terms of general acoustics, the atmosphere is largely split into two main factors..... the "whole stadium" acoustics and "home-end" acoustics. The traditional home-end of British football grounds is where the bulk of the chants start, grow, project out onto the pitch and are then largely taken up by the rest of the stadium. It is essentially the engine room of the stadium's atmosphere in terms of chants/songs, and some stadiums have 2 home ends, with the away fans tucked away on the sides to minimise their effect. The South stand was sold to us as our "Blue Wall", and is supposed to be reminiscent of Dortmund's South tribune (or yellow wall). They have obvious similarities, but the main differences are that the whole of the Yellow wall is standing, it also has something like double the capacity of our south stand (if you include corners) which although large in appearance, is just 63 rows. The other thing is that their roof is less elevated and slightly pitched downwards..... meaning it has greater acoustic catchment across a greater depth of rows. So when chants start the reverberation is much stronger and take-up is greater too. I sit in the SW corner and regularly see lots of the lower tier trying to get chants going, but having little or no acoustic leverage (being so distant from the roof) means much of their efforts are largely wasted, as they often don't reach that threshold where the chants are taken-up by the whole lower tier, nevermind the upper tier. Of course, when everyone is up for it, or the game prompts, there is a good resonance in the stadium..... and this is because the "whole stadium acoustics" of the large barrel roof and wrap around bowl gives great containment as a whole..... if the roof was extended another 10-15 metres that effect would've been greatly increased (and offered better weather protection too). At Goodison we also had in effect 2 home-ends that contributed probably more evenly than the current set up.... where the North stand is even more distant from its roof.
The away fans at any ground are generally more vociferous and unified. Giving them a corner section can accentuate that, as they can see their fellow supporters and naturally sing across each other and up into the large expanse of roof area above both the North and east stands. Corner sections can be good in that way, as you see at Celtic.... hopefully that will develop for the home corner sections too.
We're also in that settling-in period where people are still getting used to their new surroundings and new neighbouring fans etc. Hopefully as the season progresses and bigger games come along, some with greater jeopardy.... that atmosphere will grow. When it gets going it can, and will be very loud.