It's a crude way to describe a game, perhaps, but imagine a Grand Theft Auto-alike that was as freeform vertically as it was horizontally. That goes some way towards describing Microsoft's latest salvo for the Xbox 360, which has been overseen by one Dave Jones, the daddy of both the Lemmings and - surprise! - Grand Theft Auto franchises.

Crackdown takes place in a futuristic city that's split into three segments, each of which is overrun by a criminal gang. The gangs each have a Kingpin, who you must topple, but you also need to take out its Generals. As a rule of thumb, knocking the Generals off first makes it easier to get to the Kingpin, but as this is a freeform game where you can do pretty much what you like, there's nothing to stop you discovering and targeting the big guy first.

Given that each of these gangs has different areas of expertise, it's perhaps fitting that you're a genetically modified agent working for The Agency, with the support - assuming you don't take potshots at them - of the local peacekeepers. At the start of the game your abilities aren't much to brag about, but as you progress you can build up your agent's skills in five key areas: agility, driving, weapons, explosives and strength.

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Building these skills is crucial to success in the game, because to access the brains behind at least one of the gangs requires an ability to scale very large buildings, which is only possible should you have boosted your ability to the point where you can leap high enough to do so (in fact, much of the game is about scaling buildings, courtesy of the massive skyscrapers that dominate the skyline).

Likewise, you'll find it useful to have your strength at a point where you can lift large vehicles, if for no other reason than to make stepping stones to higher platforms. Or, of course, you can throw them at innocent bystanders. Ahem.

It's not tricky to build up your skills to the higher levels, but it does take a little time. And it's while building these skills and exploring Pacific City that Crackdown scores its biggest points. It's a little frustrating at first, as it's not a city where a weak agent can thrive, but leaping up buildings, gunning down enemy agents and generally exploring is exceptionally good fun. And we had a great time playing a pseudo-game of Frogger as we leapt from tall building to tall building.

But there's a problem. And that's that when you get too strong, too agile and too built-up, things really start to tilt too much in your favour, to the severe detriment of Crackdown's long term challenge. We got to the end screen within a weekend, and while it was - for the most part - one Hell of a couple of days, it was disappointing that the last few bosses proved to be the easiest to defeat, such was the effectiveness of our weaponry and agility.

And while Crackdown leaves lots to explore once the gangs have fallen - there's the small matter of finding and collecting several hundred orbs, for instance - it's never quite the same as when you're building up your strengths.

Still, what we're looking at here is a very effective freeform action game that for once doesn't pale when compared to GTA, which dominates the genre. At its best it really is quite brilliant, and few who fork out are likely to feel short-changed. But let's hope the hinted-at sequel emerges and serves up a slightly sterner long term challenge that this debut for the franchise ultimately manages to deliver.

A wildly entertaining game at best, albeit one with limits. Still, Crackdown effortlessly justifies its asking price, even if it falls short of the immense potential it shows.