Aqua Dig

Ever heard of a fellow named Jacques Cousteau? No? He's only the most famous undersea explorer in the whole world ever. Ah, that's jogged your memory. Old French bloke. Fond of water. Hit with the ladies.

Playing Aqua Dig won't make you as cool as Monsieur Cousteau, but it'll give you an idea of what it's like to venture beyond the local paddling pool and into the deep blue sea.

Then again, maybe not. Jacques Cousteau dedicated his life to marine conservation, whereas the goal here is to plunder the ocean for all its natural resources. Taking the helm of a drilling submarine, you use these precious minerals to pay for upgrades to your vessel, each of which enhance your effectiveness underwater and allow you to harvest even more riches.

These upgrades fall into five categories – oxygen tank, engine, cargo hold, sub hull and drill – and each has a distinct purpose. The oxygen tank, for example, enables you to stay underwater for longer periods, whereas the cargo hold means you can stash more goodies before having to surface and flog them. But by far the most important upgrade is the drill. The earth's crust becomes harder and more resilient the deeper you burrow, so you're gonna need a bigger drill to survive in this game.

In terms of audio and visual, Aqua Dig is a no-frills affair. There are no sound effects to speak of, which is just as well considering that the sound of drilling would be as irritating as, well, the sound of drilling. But there is a pair of tunes with a catchy lo-fidelity vibe (think Del Boy Trotter playing a synthesiser). The graphics, meanwhile, are clear and perfunctory; your little yellow sub chews its way through layers of sand, ice, and granite, and the animation is minimal to the point of monotony.

But the way it plays is what counts. The most compelling thing about Aqua Dig is the constant conflict between your greed for more riches and your dwindling supplies of oxygen. That last piece of gold you've been holding out for might cause your sub to crash at the bottom of the ocean, and, crucially, the controls are precise enough that they can't be blamed for your own shortcomings.

There's a strong puzzle element to the experience, as well. The sub can only burrow left, right and down, but can't drill upwards. Together with the unbreakable rocks that block your path, it means reaching some of the most precious minerals will require quite a bit of lateral thinking.

Unusually for a mobile game, Aqua Dig necessitates long-term engagement and saving your progress at regular intervals. The further you advance, the higher the stakes, and losing your sub means losing all the upgrades and money you've accumulated. While this is a great idea, it's unfortunate the save system is limited to only one profile at a time. It means scrapping your game and starting over if you want to improve your dive times.

But why would you want to improve your dive times? Because of the online leaderboard, that's why. Otherwise known as 'connected single-player', once you've completed the game you can email your final score (carrier charges apply) to be logged with the global leaderboard. Reaching the top of this board won't lead to fame and fortune, but the option to compare your performance with others adds a little extra spice to the challenge.

Jacques Cousteau might not approve of Aqua Dig's environmental destruction, then, but we certainly do. We especially like the balanced difficulty curve which rewards long-term play. If you'll excuse the pun, this is a thoroughly decent game, with plenty of hidden depth.