The movement is the first thing you'll notice. There's no need to discuss the control scheme, because every button you press will do exactly what you expect it to - or what you would expect it to if you ever stepped out of the flow to bother analysing what you're so instinctively doing. There's none of the Prince of Persia's flamboyance here. Instead Ryu effortlessly executes the same wall springs, back flips and handstands with his own cold, muscular precision. Gaiden is built on the same triforce as Persia - move, think, fight - but the balance, tone and execution could hardly be more different.
The game's setting is a glorious mishmash, lumping cherry-blossom samurai in with laser-cannon tanks and mystical monsters with thin-lipped men in Humphrey Bogart mackintoshes. The incongruity of the elements makes exploration all the more compelling, since there is genuinely no way of guessing where you'll end up next. It's worthwhile, too, since all sorts of treasures and puzzles are secreted around the vast levels. Your manoeuvrability is key, since many of them will be balanced on drainpipes or hidden over rooftops. The initial inaccessibility of some of these areas will fuel your desire to backtrack, as obtaining the warhammer or the incendiary shurikens will trigger memories of likely-looking cracked walls you bypassed levels ago.
These diverse environments, built with the most gleamingly detailed solidity ever coaxed out of the Xbox, aren't empty. Bands of enemies patrol, armed with nunchakus, bazookas and explosive darts, and many will defeat you first time round. However, familiarity will not dull your hunger for the humble brawl. You'll come to develop an enthusiastic affection for the few enemy groups that respawn, experimenting and refining each time you run (or spin or slice or cartwheel) into them. As the game progresses Ryu finds, buys or masters new moves, spells and weapons. Your repertoire rapidly expands from the slash-block-jump of the opening level to encompass diving decapitations, body slams and fireballs. Special attacks, fuelled by globes released by felled opponents, let you stitch together ecstatic attack sequences, blood fountaining as you tumble and twist in mid air.
The camera system provides you with a quick-centre control, which ensures you never stay disoriented for more than a moment. Periodically, however, the camera closes in and limits your viewpoint to a few feet in front and behind. Trying to fight, flip and fend off three fighting and flipping ninjas when your field of vision is so severely reduced becomes a test of how psychic you are about what's happening off screen, not of how well you've honed your skills.
These moments are the exception, however. The rule is that what will defeat you is the smartness of the enemies and slowness of your brain. As the conscious effort to master combos and counters begins to pay off, your instinctive use of them will give you time to study the moves and tactics of your opponents. Only when knowledge, skill and instinct are working in perfect unity will you be able to triumph. And against Gaiden's spectacular bosses, the challenge is amplified to crushing proportions.
The brutal fact is that a good percentage of Ninja Gaiden players will hit an impassable difficulty spike, not five hours or five days into the game, but after around 30 minutes. The first boss ups the ante tenfold from the fights that precede it, and many players will fall and fall and fall again at the arsenic-coated barbed wire of this first fence. Tecmo's refusal to extend any kind of handhold to less dedicated players is simply a failure of design, not a badge of hardcore honour. The sheer quality of Ninja Gaiden proves the existence of an immense supply of talent and invention at Tecmo, and it's impossible to believe they couldn't have found a way to increase the accessibility of the game without undermining the gloriously intractable nature of the challenges it contains. A training arena, of the kind common to the 3D fighters that Ninja Gaiden draws from, would have provided some respite from repeated defeat and encouraged players to persevere on the hard and rewarding road the game lays out ahead of them.
To applaud Ninja Gaiden for being hard is to miss the point - not least because there are portions of the game that aren't. The point is that the fluidity of movement that felt so ground-breaking in Prince of Persia only a few months ago is something which Gaiden supplies with almost contemptuous ease. The point is the dozens of things that are done so well you don't notice them happening - the perfectly judged auto-aim, the sound design packed with information and atmosphere. The point is that while it could be argued that no game has the right to demand of you what Gaiden does, few other games offer such exceptional riches in return.
Ninja Gaiden is out on Xbox on 14 May