A bug-bear of mine is football stadia that are too big for football. I’m thinking of “olympic” size stadia used in far-east, European and other world-cup tournaments (or god forbid Ozzie rules games) that have running tracks and semi-circular ends and the like, just too much space between the crowd and the game. Those that do fill up can create some kind of atmosphere, but not one that has anything to do with the game. One of the reasons why Old Trafford, Stamford Bridge and White-Hart Lane remain so good, despite their large seated capacities.
Now, terraces are a whole ‘nother story.