Why is that game is addicting? Its like it has everything for a good rythem beat game (love the ability to listen to the songs anywhere)
I don't know, it's just a lot of us like listening to music and it gives us a good chance to pay attention to it and have fun with it.
It's a challenge. I'm #1850 in Ctb (out of 100,000 players). It's a challenge keeping that rank, even more so getting higher.
This ^ It's really fun to try to climb up in the rankings, I like to set goals for myself. (currently around 37k out of 1.1 million in normal osu) Also, most people like music, and it's a great way to listen to some of your favorite music and play at the same time :P Additionally, it's one of those games that's quite difficult at first, and you need to practice a lot to get good at, so there's a big motivation to keep playing when you first start, because you want to improve.