Quarth is a conversion of a 1989 Konami arcade game, released as "Block Hole" in the US.
Randomly configured shapes are scrolling down at you from top to bottom, and you must shoot small square blocks up at them to form squares or rectangles. Once you form such a shape, all the blocks that form it will disappear, and the count will be subtracted from your stage goal. If, however, you don't manage to make a desirable shape out of one of them before they reach the bottom of the screen, it's game over. As the screen is dematerialising a shape, it stops scrolling, which gives you valuable planning time and your ship is capable of firing up to three blocks at a time.
A wrinkle in the game's mechanic is that you can get power up items by making larger shapes than those initially outlined - for example, if the shape coming at you is three blocks deep, and you make it six blocks deep before completing the square or rectangle. The bonuses you can get include the ability to slow the scrolling rate, temporarily stop it from scrolling entirely, or clear all the shapes currently on the screen.
The game has three difficulty levels, and nine stages within each of those. In order to complete a stage, it is necessary to eliminate enough individual squares (by forming shapes) to reduce the stage goal to zero. Level One of difficulty level one has a stage goal of 750, for example. Quarth also has a two player mode via link cable, but unfortunately I don't have a second cart to test this.
Quarth is good old-fashioned fun. It's ideal Game Boy fodder - simple and quick to play with functional graphics that don't overreach the capabilities of the system. Music and sound effects are unremarkable, but not actively annoying, and the controls are tight. You'll never be blaming the interface for those low scores, only yourself and your attention span.
The game is also available on Famicom and MSX, if you care to expand your Quarth collection. A little birdy told me not to expect it to be cheap for MSX, though.