I rarely give 10's, WTF deserves this rating. It is the best PSP game I have come across and possibly my favorite game.
First and foremost, WTF is a collection of mini-games. You play these games like they are "jobs" and you get a check after each game is completed based on how well you did on that game. With the money you get from the checks you are able to go to the vending machines that each have their own costs and buy items. These items are random and they range from useful tools (such as a psp light or Ramen Timer) to random plastic figures, to new mini-games.
Early in the game there aren't too many games but once you get the hang of them you will make money pretty quickly and be able to head to the machines to pick up new mini-games. The timing is spaced out perfectly. It seems that the game doesn't want to give you all the games early on and keeps you playing to make more money yet does't make it completely impossible to get new mini-games. Some mini-games are a lot more fun than others, some of them are hard, some of them are easy, and some are just flat-out bizarre.
There is an in-game mail system that you receive from various people or "friends" that you have. You will get mail telling you some hints on certain games, and other mail just telling you a bunch of random stuff. The humor in this game is great. You sort of have to have a sense of humor that fits with the developers of the game to really get some of it but I have found myself laughing many times either from mail or from a mini-game.
The game is highly Japanese based and some of the mini-games are either animeish or just pictures, while others have pretty amazing graphics for the PSP. I have spent many hours earning money and trying out the large number of games available to you towards the end. The replay value is huge. This is my girlfriend's favorite game too and she doesn't even really like video games!
If you like Japanese stuff, or mini-games, or a nice pick-up game you can play in short bursts, crazy humor, or even just own a PSP, you NEED to have this game!