Bringing a PSOne classic to the PSP proves to be a bit flawed.
Overall, the PSOne game seems to be much easier than this one. That could be because of several things. One is that you can only have 3 gadgets, and most likely you will have the Stun Club and Monkey Net taking up two buttons, so there's only room for one more because the X button is now used to jump. But these controls work rather well. But some gadgets have problems. The Slingback Shooter's aim seems to be off a little bit, causing difficulty in shooting specific targets. The Monkey Rader is a little annoying to control before you get the hang of it, too.
Another major flaw, that isn't new in the series but is worse with the PSP version is the camera. When you use the RC Car, it's very difficult to follow it because you use the camera angle buttons to control the car. Sometimes, pressing the L button to center the camera just doesn't work properly.
The levels seem to be just the same, although some requre less monkeys to be caught than the original, which can be a good thing. But some levels are just difficult to get past. One example is Monkey Madness, the last monkey-catching level of the game. Not to mention this is just a very long level, the part when you ride on a roller-coaster to a haunted house is challenging because you can't see the road blocks until it's too late.
WIth flaws aside, Ape Escape: On The Loose proves to be a fun game. If you're a fan of any other game in the series, definitely check this out.