The best place to start is with an examination of the control system. For anyone who hasn’t played a Space Invaders game before, the premise is simple. You are a lone ship sent out to destroy wave after wave of invaders from (of course) space. Your movement is restricted to the x-axis and you can shoot just one bullet at a time. If you hit an enemy your bullets fire at a quicker rate. This is how level 0 of Infinity Gene starts. The Graphics are magnificent in their simplicity. A pitch-black background and the iconic shapes of the invaders – drawn in pure white and moving ever so slowly towards you – are crystal clear. This is the image that was burnt into the retinas of millions of players over thirty years ago. This is Space Invaders.

Suddenly the screen cuts to a dazzling white. Your ship changes shape, a quote from Charles Darwin explains how it isn’t those who are strong that survive but those who are the most adaptable. Another clear-cut change of style paints the sky grey and so the game begins. Stage 1-1; nothing stands in front of you. The screen is suddenly filled with invaders. They fly in from all sides, the same but also different. They are quick. They shoot at random intervals. You are still stuck on the x-axis and you can only move by sliding a finger left and right on the touch-screen. Your ship shoots automatically, movement is your only concern. Then your instincts ignite the desire to destroy everything in sight. The feeling of euphoria rushes into your brain and you remember just why this genre is such a thrill and why it is so much fun. This is Space Invaders.

Except that it isn’t. It’s more. Here is the scenario, you complete a level. It takes approximately 30 seconds and you have decimated the invasion placed in front of you. The letters E-V-O-L-U-T-I-O-N scroll slowly across the screen and you are taken back to the start menu. A branch grows from Stage 1-1 and you are rewarded with a bonus item. It’s not long before one of these bonuses grants you free movement across the entire screen. Already we have broken into the y-axis. Taito have avoided the issue of your thumb cluttering the screen by allowing you to touch anywhere on the device. Some clever design means that the vast majority of invaders will be placed higher up the screen, so you can control your ship with precision from the bottom of the touch-screen. It's as elegant a solution as is available at the moment and does not affect the quality of Infinity Gene one tiny bit. Then you earn a new weapon to select (one of many, each of which can be upgraded during gameplay and all of which bring a unique shooting mechanic to the game) and a new level; the end result is the incredible progression of a franchise more than 35 years old. Other additional bonuses include sound-effect menus, galleries and a unique selling point: the ability to play an original level created on-the-fly to any of the music stored on your device. That means Prodigy, Norah Jones, The Arctic Monkeys or Mozart. Whatever you want, Infinity Gene will rip a level on-the-fly for you to play along to. This surely can’t be Space Invaders?

But it is. Reinvigorated and re-tooled for 2009. The score mechanic focuses on chaining together kills. Pin-point accuracy is eschewed in favour of the speed at which you destroy your foes. Kill quickly enough and you will rack up huge points, the more points you achieve the more you ‘evolve’ your game. This mechanism encourages replaying the early stages of the game for further rewards. Multiple extras are unlocked each time you ‘evolve’ a level. It is a simple mechanic: the more points you get, the more quickly a bar at the bottom of each stage result-screen fills up. If it reaches the top on completion of any given stage you earn a reward at that time. To further illustrate the point, a new (but also a tribute to the old) play style, the ‘Nagoya Attack’ has to be unlocked by evolving the correct stage. This technique scores very highly and is based on the ability to fly through enemy bullets for a split-second just after they have been fired. It’s a beautifully dangerous mechanic, a perfect example of classic risk-and-reward gameplay. Yet all this style and all this fun would have been wasted if the levels hadn’t evolved. Thankfully, they have.

Stage 2 ‘evolves’ into a moving, scaled background reminiscent of the more translucent stages of the Treasure classic, Radiant Silvergun. You’re flying through space and vanquishing everything in your path. You need to be free of the x-axis because enemies attack from every direction, there are spirals of death, lines of death and homing circles of death. The action is upped considerably and you feel more like you are involved in a Cave bullet-hell game than a sedate blast from the past. Every once in a while you suddenly remember you are playing on your phone on the way to work, you’ve missed your stop on the bus, the incredible soundtrack is all you can hear and your face is contorted into unsightly shapes while you weave your ship in an out of oncoming fire. This is absolute gaming bliss. You keep expecting to have a problem with the touch-screen controls but you never do. You can put your finger anywhere on the screen and glide your ship between the crossfire. The slide mechanic is accurate (and it really needs to be in the later levels) so that you will never feel like you have died unfairly. You died because this is Space Invaders, and it will kill you.

You will need skills you previously thought unnecessary for this, the most old-school game around. Huge battleships, still meticulously drawn in clean, white lines, will pass either side of you while tiny invaders fly from their hulls. You will need to focus your attacks on large, dangerous enemies, while avoiding bullets from tiny, agile ships. You will also need to take down bosses. Screen-filling, bullet-curling bosses, whose frequency and strength increases dramatically throughout the game. The adrenaline pumps through Infinity Gene so much you’ll wonder where the time goes and why the back of your device is now covered in sweat. It’s tense, fun, challenging, beautifully designed; it sounds incredible and quite simply it’s still Space Invaders.

There is nothing else you need to know. If you own an iPod Touch or an iPhone you absolutely need to purchase this game. The feeling of progression it offers, the updated and refined formula, the engrossing ‘one more go’ gameplay and the style with which it has been implemented are unrivalled on the platform. It doesn’t need to be repeated any more. This is the Infinity Gene.