Japanese developer Tetsuya Mizuguchi has made quite a name for himself with games like Rez and Lumines, games that combine music, graphics, and gameplay with a verve unmatched by any of his peers. This wasn't originally his game though, but an amateur PC project popular online which his company signed up and expanded upon for the PSP.

The basic concept is that you control a limited number of bombs as they freefall through various abstract computer landscapes. You control one bomb at a time, aiming to detonate it at a point at which it will destroy as many nearby enemies as possible in its blast. Chaining combos becomes the only real way to earn enough new bombs to carry on.

There are several other complications though, most obviously a very strict time limit and collecting "Quicken" power-ups to increase both your speed and the tempo of the music. New to the PSP version is the ability to unleash a charge attack by keeping your finger on the fire button and create a larger blast radius. Since this is at heart still a shoot? em-up it also features some pleasingly expansive boss battles, where the larger enemies can only be injured by combos of a particular size.

Tt is this mix of traditional arcade gameplay and a perfectly balanced strategy of risk and reward that ensures there is more to the game than just its artsy presentation. There is a problem with its longevity though, but the score attack like Caravan mode does go some way to addressing it. In this aspect, as in many others, it closely resembles Mizuguchi's Rez, and indeed until that game gets a sequel this is perhaps its closest compatriot.