What is most impressive to me about Gaga isn't really her hit singles or music video success. I can't believe how much she has literally changed the game of being a pop star. She forced everyone to incorporate so much more into their music. The girls around her had to craft personalities and harness social media and pay attention to their fashion and fanbases and music videos.
When she exploded, especially in 2009, she so quickly overtook everyone and put an unimaginable gap between her and the second biggest star. She was literally an unstoppable force, not even due to her #1 hits but because of her command of pop culture. Since then, we've seen a lot of attempted spin-offs of her success (people like Jessie J), but, more notably, we've also seen the other big girls do everything they can to close the gap. I feel like pop is all of a sudden very competitive and exciting.
Just me rambling.