So far I have only played the first world of Hydroventure: Spin-cycle, but I already love it! It's great fun, it looks great even without the 3D, the music is nice, it has bosses!, and the motion controls work really well! I even go as far as to say that this game has one of the best motion controls I have experienced so far! It feels really smooth! I also like the full-tilt levels!!
Only downside is that it are all small levels instead of the big ones from the Wiiware title. But I guess they chose for small levels because the 3DS is a portable device!