Well, here we have DJ Max Portable for the PSP. I'm not trying to write a review of the game, rather explain how it works.
The simple idea of the game is to press the correct buttons on the PSP in time to the music. The blocks falling down the screen (see the screenshots) indicate which buttons to press. When the player presses the correct button then they've contributed to the song by triggering a sound. Throughout each song in the game, the button presses add everything from rhythm parts to synthesiser sounds. The more accomplished the player, the more pleasing the song will sound.
If the player makes too many mistakes then the game will exit the level/song and display a message that instructs the player to get more practice. Because of this, the game has quite a steep learning curve.
The difficulty of the game is determined by several factors.
1. The speed/complexity of the song that's playing. The faster or more parts that the song has, then the more blocks will fall down the screen.
2. The number of buttons the player has to use. The player can select to play using 4, 6 or even 8 buttons on the PSP. Personally, playing with 4 buttons so far has proven to be quite tricky!
The music you play to is graded in terms of difficulty, so initially the gameplay feels quite sedate, though after the first couple of songs are out the way the pace quickens somewhat dramatically!
So far this game has proved quite influential in terms of my project. I'll be trying to build a small concept project where the player will have to move in front of a webcam to the rhythm of the music rather than pushing buttons. So far the accuracy of detecting motion on specific parts of the screen using a webcam (see my examples if you can!) have been a bit sketchy so I'll be trying the DJ Max Portable equivalent of '2 button mode' for the time being...
So, the view the player will have is of themselves on the screen with blocks falling down over their image. When the blocks reach the bottom of the screen, the player will make a motion (I'll figure the precise motion out at some point!) over a specified area of the screen to 'clear' the block and enable them to progress through the game...
...hopefully some of that makes sense!
Videos of more talented people than me playing DJ Max Portable 1 & 2 on the PSP
(the last link will give you an idea of how frantic the gameplay gets!)
Mock-up images to demonstrate this idea - pictures are a thousand words which means there will be less stuttering from me!