i only play the keyboard mode of osu! :^( the mode is called osu! mania.
also, 10/10 recommend playing it!! if your internet ever crashes, you can still play it.
Osu is really fun. I'd recommend it. It does take a good amount of time to get decent at it. The only problem i can see with it is the song variety because although there are plenty of songs most of them are weeaboo songs or electronic.
the keyboard one is basically stepmania 2 lolol. nothing special. the keys for 4 keys are : df, jk. 5 keys : df, space, jk. 6 keys : sdf, jkl. 7 keys (which i mostly play on) : sdf, space, jkl.
also, like @KrazyKid132 said, many of the songs come from anime or just dubstep / remixes. there are a few songs though that are worth downloading. just hard to find
@kaneki From what I heard in the competition, I do like the Japanese songs, so I'm glad it introduced me to them; they have their own qualities. I'm guessing since there seem to be less (popular?) American music, that perhaps the players are not able to make their own "maps." Is that what it is? It actually seems like it would be fun to make them.
What's osu? o.0