I regularly attended games at Stamford Bridge in the 80’s.
I have been a visiting fan at Green Bay and Arlington. I use these 2 because they are the only stadiums I have visited as a Niners fan.
There is absolutely no comparison between the atmosphere at the NFL and English football games.
Big cities in the US get to see their team 8 times a year. It is a major event.
The pre-game is an event in itself. Game day crowd participation is like no other sport in the world.
I’ve sat in the stands at Candlestick Park and just recently Levis Stadium and being at Stamford Bridge against another London club just doesn’t compare to what I’ve experienced.
Would be keen to know where you have been to to watch the NFL.