Caveat: I have only played through the song one time.
The latency started off okay, a bit of lag, but manageable by shifting my input timings. But over the course of the song, the audio drifted and doubled itself — there were two sound cues for each object, increasingly far apart! By the end, the little “do-be-do-de-do! [whack]” ended before the rock even appeared on screen.
The art looks pretty good though, not a terrible Karate Joe clone.
Gonna go delete it now. But, developer: fix up the bugs, and maybe add some more Rhythm Heaven content, and I’d probably redownload!