One of the first things that's apparent about the portable PlayStation when it's seen for the first time is the screen quality. It just looks fantastic: bright, colourful, and surprisingly large. For a shoot-'em-up fan, images of a portable version of Gradius or R-TYPE immediately fill the mind; the screen just seems perfect to play host to such a game...

To date though, a Gradius or R-TYPE game has yet to appear on the pocket SONY, but with the release of Sengoku Cannon: Sengoku Ace Episode III, it does now have a horizontal scroller to call its own.

As the subtitle suggests, Sengoku Cannon is the third installment in the Sengoku Ace series. Although traditional shmup fare, the series is noted for being a bit different due to it featuring Shogun characters and a feudal Japan setting. The original game was a vertical scroller, but for its better-known sequel, Sengoku Blaede, the action was rotated 90 degrees. This new addition to the series continues with the horizontal format - a logical decision when you consider the widescreen dimensions of the PSP.

Given the heritage of its predecessors, and its developer - genre specialists, Psikyo - it's fair to say that Cannon arrives with a certain air of expectancy and much to live up to. First impressions are initially good: The excellent artwork, character design and overall Japanese flavour that the previous games are noted for is all present and correct, and also backed-up by some great music. It's only when you actually play the game do the problems begin to arise.

The first thing that sticks out is just how small the player sprite is. Which isn't a real problem in itself, but when combined with the overbearing scenery of the opening stage, it can be very easy to lose track of where your character is, and indeed the enemy sprites. The controls don't help the cause either: Whether the D-pad or analogue "stick" is used, player movement remains extremely twitchy and vague, meaning the player never feels "at one" with the onscreen avatar - not ideal for a shooter with many "bullet hell" situations.

The problem of losing the character in the scenery starts to evaporate once Stage 2 is reached, since that, and subsequent stages, are more plain in appearance (too plain, it could be said), but the vague controls still make bullet-dodging tougher than it ought to be.

A couple of things help to make life easier for the player though, the first being the hitbox of the character, which is very generous and allows for narrow escapes from instant death. The second thing is the cannon shot from which the game takes its name.

When enemies are destroyed using the cannon shot, any bullets they fired are transformed into harmless gold coins which earns the player bonus points. This addition is the main gameplay "hook" to the game and it works well, adding a layer of depth to what would otherwise be standard shmup action.

The Boss battles are also particularly good and the most entertaining part of the game. Avoiding the mass of bullets and projectiles that are thrown in your direction is always satisfying, and doubly so if a watchful eye can be kept on the damage meter to finish them off with the cannon shot for a bigger score. Like many shmups that feature humanoid characters, they're preceded by a bout of smack-talking (Japanese) dialogue with your opposite number before the action begins.

For all its faults, Sengoku Cannon still remains fun to play if not taken too seriously, but there's no escaping the fact that the experience is forever tinged with frustration at how sloppily it's been put together. It could, and should, have been an excellent game, but in the end, it's merely average and a big disappointment.