Nothing more and nothing less.....a beautiful melody line and good lyric.
Singing along is totally optional for us (besides the fact that many will mess up the words). As you mentioned, it is not an easy song to sing along. From a purely mechanical/technical point of view, the singer has to have a very good range with good power at both lower and higher notes...as well as a high degree of control.
More then anything, much like where this whole controversy rests...it is symbolic. The flag and the anthem unite us...they are apolitical....until recently.
~Jeordam