In addition to the lengthy single-player adventure, there are also minigames you can play with a friend, such as snowboarding (with monkeys), boxing (with monkeys), and Ping-Pong (yes, with monkeys). This is a nice addition, but the games aren't deep enough to really stand out as a major feature in the package.
Graphically, Ape Escape: On the Loose is closer to the PS2 release of Ape Escape 2 than it is to the original Ape Escape. The monkeys are bright, colorful, and full of life. The game has a very cute, kid-friendly look to it, and it's hard to deny the charm of monkeys with sunglasses toting submachine guns and laser pistols. The game runs at a smooth frame rate, though you'll notice a few dips here and there. Overall, it's a good-looking game.
The sound attempts to be just about as cute as the graphics with lots of squeaks from the monkeys and a lot of high-pitched speech from the various human characters in the game. The music is appropriately upbeat as well, and all of this ties together to give the game a little more charm.
The original Ape Escape was an amazing game, and it's a shame that some aspects of it haven't translated to the PSP too well. Still, even with the control and camera being an occasional chore, there's enough good old-fashioned platforming here to please fans of the genre.