I find that the gameplay is most "attached" to the music when a song has a strong, defined beat. The blocks may not all be blocks that I want to hit, but they'll generally show up in time with the beat, even on songs with rather erratic rhythms. I'm pretty sure it figures this out by analyzing peaks in the waveform. So you might not get results that are as satisfying with slower songs that lack percussion. (Sometimes even faster ones - bluegrass, for example, isn't a genre that plays terribly well in Audiosurf, unless the band has a drummer or they mixed the bass really high or something.)
Maybe it's more noticeable in puzzle mode, since you're hitting a greater percentage of the blocks than you would in Mono, where you're dodging around most of them?