I played it again today and figured out that you could get the lanes moving by simply holding down the arrow keys, which is a tactic that usually doesn't work in rhythm games. Still, simply tapping the keys to the beat didn't really work for me. Maybe there was some kind of latency, maybe the time window was too small. Hard to say.
But some form of visual feedback where the beat is supposed to be would probably help a lot. A click track in the beginning could also help to get into the groove. Especially songs that have a long intro without any percussion (e.g. Flower Dance) or no percussion at all with varying speed (Flight of the Bamboo Cutter) are pretty unpredictable when it comes to finding the beat.