This is ultimate rhytm game fun. I don't even know if it should be considered a rhytm game, but oh well.

Endless levels created by the most skilled level creators I've even seen across the gaming world, with some of the most iconic music on the internet.

This game definitely has a learning curve, but it's worth every minute and after you get to a reasonable skill level (I'd say beating easy/medium demons with not that much suffering) it's just so much fun.

This. This is THE BEST - I will say it again - THE ABSOLUTE BEST Multiplayer experience I ever had in my life.
I've played multiple games, competitive and casual with friends, and no game managed to be more fun, addicting, exciting, thrilling than this one.

Unfortunately, bad management, a terrible launch and little to no marketing made this into a money pit that was eventually abandoned and closed down by Velan. A fate only the worst should deserve, but somehow only achieved by the very best.

I miss Knockout City, and probably will for as long as I play online games. I'm terribly sorry for everyone that couldn't experience this masterpiece of entertainment in it's glory.

Osu! Is one of the greatest rhytm games to ever exist, being fun for almost any skill level and sorting an infinite amount of songs, especially if you're into anime, but the truth is you can find almost anything here, even if it's a crappy beatmap with unbalanced difficulty.

The skill ceiling is endlessly high and the community is alive and welcoming for what I can say in my experience.
The multiplayer modes lack an individual difficulty selection, but I understand they are more meant to be a "competitive" mode rather than a Fortnite Festival-like "play a song with your friends".