Japanese developer Q-Games should be sued under the Trade Descriptions Act. Downloadable PSN game PixelJunk Shooter, the fourth in the quirky and varied series, is much more than a shooter. It would be better titled: PixelJunk Shooter but Mainly a Puzzler, with Great Physics.

While shooting is the game's central mechanic - the shooting of lasers, homing missiles, jets of magma and water - it is not a side-on shooter in the traditional sense. It does not rely on twitch reflexes or android-like hand-eye coordination. It does not rely on the kind of skill you see nutcases showcase on arcade "shmups".

Instead, the game has more in common with Just Add Water's recent retro PSN game Gravity Crash. Smart, rather than skilful, craft movement is the order of the day. And while you need to shoot to kill on occasion, you'll mainly be shooting to manipulate the environment.

But it's easier to get to grips with than Gravity Crash. The control scheme is simple and accessible: The left stick moves your craft, the right aims, R1/R2 fires and L1/L2 deploys the grab claw. So, you can move your craft about the cavernous levels, turn so you're facing behind the way you're going, and let off some laser fire. In this way, Shooter's more like your straight up twin stick shmup. My only gripe with the controls is having to quickly rotate the right stick 360 degrees to perform a ship spin - a move that absorbs point-giving orbs and bores through vulnerable rock. Half the time the move doesn't trigger, and it's hard work on your right thumb.

Each of the three "episodes" is made up of five stages, and each of these is made up of five levels. They're all set on some mysterious planet, where a colony of energy gathering humans has unearthed something nasty. You arrive to find out what's going on, and rescue the stranded workers. Plot's not the point, of course, but it should be noted that Shooter's "story" is fleshed out more than in any previous PixelJunk game. The 1080p PixelJunk 2D graphics make the tight, winding spaces as eye-catching and colourful as you could hope for, and the breezy trip-hop music, from High Frequency Bandwidth, fits the tone perfectly.

Look at the lava. Isn't it pretty?

The gameplay, like the controls and graphics, is structured with simplicity in mind. Each level exit only opens once you've rescued all of the workers. To rescue them, all you need to do is grab them with your ship's extendible claw. It sounds simple, and it is, but it can often be harder than you think. Some of the workers are trapped in hard to reach areas you initially reckon are impossible to access and must be some sick joke on the part of Q-Games. But in some respects, the easy to grab workers pose the biggest problem. Workers are vulnerable, and in PixelJunk Shooter, friendly fire is a real danger.

Shooter's genius is environmental manipulation, and the tools you're given to do it. It comes as no surprise to discover that Q-Games toyed with the idea of calling the game PixelJunk Elements, because that's exactly what the game's about. At first, it seems overly simple. The early levels ease you into its complexities: You're able to blast away soft rock with bog standard laser fire, eating away at the level itself as you search for workers. Stray close to lava for too long, and your ship will overheat and crash - taking a dip in water cools you down. But things soon get much more complicated than that, and Shooter becomes the hard PixelJunk experience the series is known for.

When water meets lava, magic happens.

The game's first episode is lava based. Lava spews from volcanoes and gaps in the environment, spilling out and across the stages, burning everything in its path, including workers and the planet's hostile creatures. When lava meets water, it cools, turning into a rock you can destroy with laser fire. So, if a worker is trapped underneath lava, to rescue him, you need to pour water on it, turning it into rock you can shoot through.

The element-based gameplay and puzzle-solving is clever, but the superb physics unequivocally steal the show. The fluid dynamics really are a joy to behold. Lava flows spectacularly, which is a weird thing to say of a 2D game. Water cascades with a current that drags your ship. Lava is thicker and weightier than water - your laser fire doesn't travel through it as easily. Water barely affects laser fire at all. For a downloadable game, it's superbly realistic. Sometimes, you'll unleash lava and water and it'll come together so beautifully, that you'll find some place safe to sit back and enjoy the show.

Some of the later stages, however, offer no such luxury. From half way through the second episode onwards, the cavernous stages require careful movement and clever environmental manipulation to save enough workers to open the exits. You're able to grab objects that act like sponges, absorbing water and lava, and then empty them in other areas - they explode like water or lava bombs than can do as much damage to your ship as they do to the environment. Laser beam trajectory can be altered so beams bounce off of reflectors, melting ice and destroying enemies. Gas flows can be set alight, destroying vulnerable rock as it burns. Some enemies bore through the environment as they try to destroy you - leading them a merry dance is a useful way of opening up new areas. Eventually, you'll gain access to Water and Magma suits, which allow you to fire your own water or lava streams (the lava cannon in particular is brilliant). These suits also give you a special claw that can be used to pull ice formations apart. And, even later, you get access to an Inverter Suit, which allows you to enter the lava itself (the third and final episode adds another element to the mix, one best discovered yourself).

It is when Shooter combines all of its elements that its best nuances are revealed, and is most challenging. Sometimes you'll find yourself head-scratching for over half an hour, trying to work out how to melt this particular bit of ice, or reach that particular worker. Shooter never overwhelms you with mechanics, but towards the end of the game, it does expect you to have been paying attention.

Shooter's only real problem is that it feels too short, even at £6.29. The three episodes shouldn't take longer than four hours to work through. The game feels like less value, however, when you consider replayability. Once you've worked through all three worlds, the only motivation to go back and replay the stages is to improve your overall score or to lower your individual stage completion time for the online rankings. But speed runs don't sit well with Shooter's more considered gameplay. It's more enjoyable to try and complete every level without dying, rescuing every worker, eking out all the off-screen secrets and nabbing the hidden treasure. It might not be particularly flashy, but it's rewarding nonetheless.

Shooter can at times be hard, but it's easier than the previous PixelJunk games.

And the two-player co-op mode, while fun by virtue of playing with a mate, the game isn't designed to make the most of it. There are one or two nice co-op features, such as being able to rescue your on fire chum by grappling him and dropping him in water, but there's nothing that can't be done on your lonesome. And, somewhat surprisingly, I quite preferred playing the game on my own, holed up in intense, solitary confinement, forehead creased in concentration.

PixelJunk Shooter is an enjoyable, quirky game that's yet another successful entry in the PixelJunk series. And, as with all the PixelJunk games, it's right up PSN's street, a service that's fast becoming the home of the weird and interesting. There can be no doubt that the game's over too soon, but the journey is still worth travelling. When water meets lava... Well, that's worth the asking price alone.