Back around when the 70's became the 80's, music began to be played on automated equipment that made rhythm dominant and melody secondary. (The famous Roland TR-808 was launched in 1980.) That was the beginning of the end for popular music and it has been pretty much down hill since.
Most of the 'great' songs of the past 20 or 30 years will be in the dust heap 50 years from now, but people will still be singing 'Over The Rainbow', 'Moon River' and Sinatra. The great 60's bossa nova melodies of Antonio Carlos Jobim will be played forever. The Motown hits written by Holland -Dozier- Holland ,Stevie Wonder and Marvin Gaye were masterpieces of melody.
Rhythm does not last the test of time, melody does. Which brings us to today's Super Bowl show, the Black Eyed Peas. They had what looked like a cast of thousands of weirdly lit stick figures surrounding the stage, swaying to their music, and some clever lighting effects and decor on the field, and a bunch of prancing around looking energetic, but it didn't look like they had much music.
In 5 or 10 years, no one will care about this group's music anymore, take that to the bank. It is fluff of the moment.
As for Christina Aguilera, what an embarrassment. Just the sing the song, the National Anthem, in a direct and natural way, and your voice will shine through beautifully.
But no, Christina has to 'riff' on the melody because that is the style of contemporary 'soul' divas from Whitney Houston to Celine Dion to Mariah Carey to Aguilera herself. She doesn't express the melody , or compliment it, she destroys it. To contemporary music fans, who clearly don't know any better, this sounds fine. To those schooled in the great singers like Ella Fitzgerald or Rosemary Clooney, this stuff is an abomination. Bette Midler is a great singer. Oh, I forgot, she's old.
I don't dispute the technical achievements of 'modern' pop music, or even the skill of the musicians. The music itself is relentlessly second rate, with an exception here and there.