We knew the game was coming to the Wii and Playstation 2, but the Playstation Portable seems like a bit of a surprise. Though, given the multiplatform nature of the game why wouldn't it appear on Sony's portable?
Now for a little hot spoiler action as found in the ESRB's rating summary:
This is an action adventure game in which players hunt, fight, and capture ghosts and other fantastical creatures, including the "Stay Puft Marshmallow Man." Players mostly use a rifle-shaped wand that emits laser-like currents ("proton streams") to stun and trap the ghosts. Players can also shoot a green gel-like substance to weaken creatures and ghosts. Proton streams often cause environmental damage, leaving burn marks on walls and causing small objects (e.g., books, chairs, tables, picture frames, and potted plants) to disintegrate. The game also contains some tongue-in-cheek dialogue used for comic effect (e.g., "Why do the good ones always play hard to get?" and "I'll cover the elevators and escort any ladies safely to their rooms.").