I grew up playing Rainbow Islands and its successor, Parasol Stars on the Amiga. I was excited to see two versions of Rainbow Islands being made for the PSP and DS.
I believe that this version was a swing and a miss. I was disappointed to see a limit placed on the number of rainbows you can have out at one time. The 3D aspect (which is just methods to traverse to a couple of other 2D levels) seemed gimmicky, and the graphics were very disappointing for the PSP system.
Good to play for nostalgia value, but in all reality stick with the classic on the Amiga :)