The PSP version is reminiscent of Lumines, and has a total of 40 skins, which slightly "alter" gameplay. Additionally, it offers two modes of play, "Original" and "Break". Break mode differs from original in that any line segments above a completed line will drop down after that line has been cleared, which makes it without a doubt the easier of the two.
Additionally, the player is given the option in the main menu to play a 10 x 10 grid versus the default size for added challenge.
Source: Wikipedia, "Gunpey", available under the CC-BY-SA License.