Really really good! If you like games like Maimai / Chrono Circle / Project diva / Jubeat, you'll love this. It's clearly made by people who love rhythm games and knows what makes them fun to play. The tracks in the demo are great and honestly a really generous selection to get a feel for the game! 

Obviously this is only a demo, so I'm sure there'll be significantly more variety in the full version - but my only real feedback would be that this definitely feels targeted more towards more advanced rhythm game players. More charts with slightly lower speeds  / simpler charts would be nice to get to grips with the different note types. I really liked this overall though and will definitely be recommending this to my other rhythm gaming friends!