It's not been a great month for would-be assassins. Ubisoft Montreal put you in the robes of a general dogsbody and only occasional killer, and now Io Interactive has made a Hitman game where your reward for finishing a level is often nothing more gratifying than passing through a door. On one occasion, even, the fade to black and subsequent results screen happens while you're crawling through an air duct. Or sometimes the assassination takes place in a cutscene; on more than one occasion, though, your perfect kill is botched as soon as control is taken away from you. Only sometimes in Hitman: Absolution do you get the satisfaction of executing a perfect kill before strolling off unseen.

In other words, you get all the hard work - the mistakes, the experiments, the restarts, the contingency plans, and the lengthy waits through interminable NPC conversations - without the gratification of the execution. This happens far, far too often.

If it's not really a Hitman game, then, what exactly is Hitman: Absolution? Well, there's strong evidence to suggest Io has been playing rather a lot of Splinter Cell Conviction: you use your finite supply of hitman 'instinct' to outline enemies and interactive objects, or you can expend it on 'point shooting' sequences where you mark your opponents one by one, and then jab a button to execute them. With bad guys loudly questioning your whereabouts, meanwhile, you begin to wonder whether they might even start mentioning that incident at the AIRFIELD, FISHER.

Being discovered, of course, is part and parcel of every Hitman game. But your window of opportunity for extricating yourself from a tight spot was always a little wider before. Besides, if the worst came to the worst and your best-laid plans ended up in tatters, you could always enjoy the catharsis of gunning down scores of people to compensate for the frustration of starting again.

In Hitman: Absolution that opportunity doesn't present itself too often. You're rarely given the tools for a serious gunfight, not least because guards are more plentiful and better-armed than before. There are fewer rooms to secrete yourself in from patrols, and so many people milling around that getting out of a key NPC's sightline tends to involve sprinting away from one hail of gunfire straight into another. Part of the fun of the previous Hitman games was winging it when you messed up. Hitman: Absolution is no fun.

The bizarre thing is that Io seems to tacitly encourage thinking on your feet. Its lack of mid-mission saves and the sparse checkpoints - positioned in places that suggest Io is subtly guiding you down a specific route - suggest you're not supposed to simply reload and start again. But with AI this sharp-eyed and aggressive it's very difficult. There's nothing wrong with enemies providing a challenge, of course, but their sheer numbers make certain tactics very restrictive.

It makes utter nonsense out of the disguise system, for starters. Wear an outfit that should allow you to blend in with others - a SWAT vest, staff uniform, guard fatigues - and you'll find venturing too close to one of your pretend peers will instantly arouse suspicion. You've then got perhaps a second to escape their eyeline before they'll start tailing you, at which point the idea is to lure them to a safe place and dispose of them by lethal or non-lethal means. There's an understandable logic to that, but safe places are rare. NPCs constantly patrol the playspace, and even if they're not the type to alert others to your presence then your cover is considered 'blown', meaning everyone on the level will react to you unless you find a fresh disguise.

You might also raise the alert simply for the sin of not pressing yourself flush against a wall, even if there's no way the alerted party could have seen you. Worse still, one of the loading screen hints recommends a tactic that simply doesn't work: strolling casually around won't quell the attentions of a pursuer. You're actually far better moving around by constantly bobbing up and down from cover positions, as this is bafflingly deemed much less suspicious behaviour than walking.

You're best staying out of sight entirely for the most part, then, but on many levels that's almost impossible; on particularly populous stages you're as well remaining in your iconic suit for the duration. 47 also never thinks to fully suit up when disguising himself, either: when adopting the garb of a balaclava-wearing henchmen or radiation suit, he leaves his distinctive, angular face visible throughout.

Still, if 47 likes to draw attention to himself all too often, the game's lighting does him no favours, an abundance of bloom glancing off his polished dome to spray a fetching shade of blue lens flare into the player's face. J.J. Abrams would be proud. Besides that, Hitman: Absolution is an attractively grimy game with the kind of attention to environmental detail that made Kane and Lynch's Shanghai shootouts so atmospheric. It's ugly in a very pretty way, in other words.

That's more than can be said for the narrative, mind you. Yes, the changes to the Hitman formula are all in service of a story that would be offensive if it wasn't so preposterous. It's a tawdry, grubby little tale of perverts and psychopaths: men are grotesque, corpulent, seedy, and greasy, but they fare better than the women, almost all of whom are helpless victims, strippers or nuns in fetish gear, most with the pneumatic proportions of an aggressively overinflated sex doll. Constant flashbacks of 47 killing his former handler in the shower are Io's stab at emotion, but lingering soft-porn shots of naked flesh make you wonder whether he's actually upset or preparing for a bit of between-mission onanism. Talking of which, one target - offed in a slow-motion action sequence straight out of a John Woo film - dies wondering why he has an erection. Mature gaming, ladies and gentlemen.

It's not all bad. There are fleeting moments here where Io gets things absolutely right. An early highlight sees you milling unseen among an astonishing crowd in Chicago's Chinatown, with myriad ways to dispose of your target from a drug-related death to a car bomb. It's classic Hitman with a Hollywood budget. A later, sweaty-palmed motel escape, meanwhile, segues into a stalk-and-kill sequence in a darkened cornfield that nods to one of Spielberg's great set-pieces, with 47 cast as the intelligent, vicious raptor in Io's lost world. That isn't quite Hitman as we know it, but it's a rare and fleeting sign of what could have been.

As, too, is Contracts mode, a smart addition that allows you to design your own hits to be shared with friends. The idea is to compete to become the most silent, deadly assassin, and while it doesn't entirely salvage the weaker stages - there's no salve for poor level design, it seems - it's something of a saving grace for Absolution as a whole, and a place where the classic 'separate and eliminate' tactic stands a greater chance of actually working.

The problem with Absolution is that its new custodians from the Kane and Lynch team seem to have fundamentally misunderstood what made Hitman great. If Io was attempting to make it more accessible then it's almost entirely failed, with more restrictive, prescriptive and awkward design allied to a challenge that is pleasingly firm but often infuriatingly unfair. If the desire was to make a Hitman for the purists, well, it's failed there too: the segmented sandboxes here simply aren't as expansive or as flexible as before. Hitman wasn't great because it was hard: it was great because it rewarded curiosity, experimentation and invention. This is what genuinely mature gaming is all about, not swearing, tits and gratuitous unpleasantness.

Occasionally you'll witness flashes of brilliance, glimpses that suggest Io could yet salvage something from this wreckage for its next Hitman game. And then you finish a stage with a tedious quick-time event, snapping the neck of a morbidly obese Danny Trejo-alike in a wrestling match watched by hundreds - astonishingly earning yourself a Silent Assassin rating in the process - and you shake your head sadly and wonder how it all went so badly wrong.

Version Tested: Xbox 360

This review was written after spending 18 hours with a retail version of the game provided by Square Enix. Story mode was completely finished and numerous Contracts missions were attempted.