Kinda surprised I didn't see a thread in the first 3/4 pages of this section on Audiosurf.
Tl;DR, its kinda like CtB on the track for 3key mania. But with way better graphics. And blocks to dodge instead of catching everything.
There a few different modes: Mono and Ninja are basically the same, then theres "wakeboard" where you can jump off the track and do tricks of sorts when the chorus starts or when a large moment in the song happens. Theres also one that has you controlling a person running down a track and dodging under/over obstacles.
Its a lot of fun though, and you don't have to worry about beatmaps because the song auto generates maps for each song. Each runthrough will have the same notes, but the position in the three lanes changes each run.