The colorful world of Sackboy and friends translates very well on the PSP screen. Sure, the game is missing many of the lighting and particle effects that make the PS3 game look so good, but considering PSP's limitations, this is an incredibly good fascimile of the original. Even in its early state, the framerate holds up surprisingly well. Even more surprising: it appears the game's use of physics has been largely retained.
If the demonstration level at E3 is any indication, it appears PSP owners will be able to create levels of equal complexity as on the PS3. The level we played showcased the requisite spins, swings and grabbable sponges so integral to the LBP experience.
One gripe we did have with the demo available at E3 was the controls: the PSP analog nub isn't ideally suited for 2D platforming. Switching between the three layers of the PS3 version was frustrating enough, and the PSP nub confounds the problem even more. On the DualShock, the D-Pad was reserved for expressing emotion on one's Sackboy. We'd love to see PSP owners to have the option of making the D-Pad the primary input for platforming.
Although it's not being developed directly by Media Molecule, it appears the PSP version of LittleBigPlanet is coming along smoothly. We still have to test its creatior tools, and see how well the wi-fi functionality works. So long as the handheld game can provide the same amount of polish as the console game, LBP can become yet another "killer app" for the PSP.