For me, it's going to take one hell of a 2D shooter to prize my bleeding eyes away from that other Xbox LIVE Arcade exclusive downloadable 2D shooter, Bizarre's stupendously addictive Geometry Wars: Retro Evolved 2. Is Galaga Legions, the latest in the 27-year-old (dear God!) series, the game to do it? Unfortunately it isn't.

Why? Because while it's gameplay is irrepressibly unique, and addictive in its own right, it's wafer thin in the stuff to do stakes.

There are two game modes in Galaga Legions - Adventure and Championship - but for all intents and purposes they're exactly the same. In Adventure mode you fend off the Galagan horde across five areas, each with five levels, that get harder as you progress, starting in area one. In Championship mode you can select which area to play from the get go with a view to nailing a wicked score, but they're the same five areas as in Adventure.

So, at the end of the day all you've got is five areas to play, and the way you play them is exactly the same. In Retro Evolved 2 there are loads of game modes, each one changing the way you play. See what we're getting at?

The gameplay is addictive and deep

If you're going to take a punt on the game it's going to be because you enjoy the core gameplay so much that it makes up for the fact that there's not much to do. For the series' legions (couldn't resist, sorry) of fans this will unquestionably be the case, and that's because the core gameplay is a compelling mix of razor sharp reaction and solid strategy you won't find anywhere else.

You control your craft with the left thumb stick, as you'd imagine, and can move it all over the screen (in the original Galaga, also on XBLA, your craft was fixed at the bottom of the screen). With the right thumb stick you control two friendly satellite ships. These ships, which act as moveable turrets, need to be strategically placed so that they mop up the waves before they've had the chance to say hello.

Galaga Legions is all about right angles. You can only shoot up, down, left or right. While this initially feels quite restrictive, you soon realise it's part of what makes the Galaga gameplay so unique, and entrancing. The game displays the arc a Galagan wave will take a couple of seconds before it appears on screen, giving you the chance to position your turrets at their most effective point. What Galaga Legions eventually evolves into is a frantic game of planning ahead as you desperately try and place your turrets in the path of future incoming waves. That your turrets fire more rapidly the closer they are to the Galagans makes that game even more dangerous. Imagine playing Galaga with Nicolas Cage's character's pre-emptive power from Next. That's what it's like.

Helping you out is a new vortex super power, triggered by shooing a floating power up that sporadically appears in the leves, which takes any enemies sucked into it and converts them into friendly satellites. Unlike your two base turrets though, they don't last forever, so once they've touched an enemy they're gone. But it's pretty cool, and extremely useful, to have a small army of Galagans at your disposal.

Unfortunately there's not much meat to Galaga Legions

That's because things can get very busy on screen very quickly. Sometimes there are so many Galagans on screen at the same time that it can feel like you're being overrun by an army of ants. While the frame rate does struggle when this happens, or indeed when you die (which will happen, a lot) it's not something that's going to bug you too much, and certainly doesn't affect gameplay. Yes Legions is a new game but it's unashamedly retro, and as such is brutally difficult. But that just makes it all the more rewarding.

Like we said, our biggest problem with Galaga Legions is with what it doesn't have, rather than what it does have. The genius of Retro Evolved 2 is that as soon as you've booted up the game your friends' scores are displayed for each game mode, and where you figure in the mix is highlighted. Right off the bat you can see if a mate of yours has beaten your Pacifism score, or whether you're still top dog in Deadline. While Galaga Legions does have online leaderboards for both the Adventure and the Championship modes, the game makes no effort to hook you in with a competitive incentive. When you add to this the fact that there's no co-op, or competitive multiplayer modes of any kind, Galaga Legions can become a lonely experience.

Still, for hardcore shooter fans, Galaga Legions is an essential purchase, and can rightly be considered the definitive Galaga game. For everyone else, we can't recommend it over Retro Evolved 2, which remains the Xbox 360's best shooter by a country mile.