Pity poor Koei Tecmo and developer Omega Force, who’ve found themselves in quite the bind. The musou games, so it goes, are ones that refuse to change – an immobile force that, instead of evolving, simply undergo a costume change whenever the mood takes them. One day they’ll show up for work in a hulking mech suit for the enjoyable Gundam spin-offs; the next, they might don Link’s green hat in the well-received Hyrule Warriors. It’s a formula that’s constantly adapted, and seemingly never-changing – underneath those cosmetics, the well-oiled musou machine grinds away relentlessly.

And yet, for those in thrall to that machine, there’s a mechanical beauty deep at the heart of these distant cousins of classic arcade brawlers such as Golden Axe, Final Fight and Streets of Rage. Omega Force takes that same spirit and outrageously embellishes it, until you’re a swirling dervish in the midst of a crowd of hundreds. After all, who doesn’t like a good dust-up? Even better when it’s tied to a game of ruthless optimisation, where you’re trying to clear a map as efficiently as possible as you level up members of the impossibly large cast. In all that chaos there’s something soothing to be found; if you know what you’re looking for, there’s something quite excellent there too.

Maybe it’s a symptom of over-familiarity with Omega Force’s industrious output – if you’ve inclusive of all the various spin-offs and side entries, it’s easy to count over 50 entries in the series since its inception – but these remain games with more detractors than devotees. Dynasty Warriors, the vanguard of the musou genre having helped start it all some 18 years ago, has born the brunt of the criticisms in recent years, and Dynasty Warriors 9 now has to take the strain of the series’ reinvention. It’s a fairly unimaginative reinvention, at that; this is an open-world game, the more familiar musou action pasted thinly across a staggeringly vast depiction of Three Kingdoms-era China.

And, as an open-world game, Dynasty Warriors 9 falls miserably flat, mistaking breadth for any kind of meaningful depth. You can take to your horse and ride from one end of the map to another in a feat that’ll take up to two hours – although you’ll have fallen asleep in the saddle well before then. It’s a map with plenty of scope but not much by way of spectacle, or satisfying diversions. Yes you can hunt, gather resources for crafting or even purchase your own hideaway to decorate with trinkets – because, well, that’s what other open-world games offer. Dynasty Warriors 9 too often feels like a pale imitator rather than having its own sense of purpose.

So there are watchtowers to climb and a map that’s slowly filled in over the dozens of hours it takes to see through it all – and there’s a lot to see through, with some 83 characters to tinker with throughout the campaign. Dynasty Warriors games aren’t exactly new to excess, of course, but the endless list of side missions – none of which gets that much more advanced than going to a certain destination and dealing with a mob or two – and hollow distractions makes it all feel a lot more like bloat.

Dynasty Warriors games aren’t exactly renowned for their technical prowess, either, but this is surely a nadir for Omega Force. There’s ambition – the map is sizeable and seamless, taking in towering mountain ranges, open fields, thick forests and castle courtyards – but it’s spoilt by appalling execution. Dynasty Warriors is, to put it bluntly, a mess. Played on a PlayStation 4 Pro there are sudden lurches in the frame rate, and the dreary backdrops and stuttering traversal animations don’t really account for such sickly performance. Even worse, it detracts from the action that’s the meat of any decent musou game.

Which is a shame, as the core musou mechanics hold up, and this time out there are some fine adornments. A new combo state system allows you to easily flow through encounters, while a trigger system gives easy access to stuns, launches and knock-downs. It makes for faster-paced combat, propelled by those additional systems that help you endlessly juggle waves of enemies without interruption. When you’re caught up in the perpetual motion of a battlefield that’s asking to be danced through, it’s heady stuff.

Those open world elements don’t really enhance the core, though, and more often clash rather complement the thrill of a good musou game. There are ill-advised stealth sections, and a grappling hook lets you scale walls and sidestep some of the encounters as you head straight for your mark – all of which seems to be missing the point somewhat. Too often Dynasty Warriors 9 feels like a half decent series entry that’s been chopped up and dispersed over a half-arsed open-world map.

But then there are the occasional moments when you understand what Koei Tecmo and Omega Force were striving for here, and when it all clicks in place. When you’re galloping through soldier camps to the front lines and volleys of arrows suddenly darken the sky. When you’re riding into battle with your fellow generals by your side to go and capture a castle, or just seeing the romance and sweep of the Three Kingdoms saga writ across vast acres of land that’s yours to conquer – even if it’s writ in a scruffy scrawl.

A shame, then, that it’s often undone by technical failings and shoddy execution. There’s plenty of room for refinement in the future, but this is a sideways step for the series rather than a truly progressive one. Dynasty Warriors 9 isn’t going to win the series any new fans. The big danger is it’s going to alienate a fair few of the existing ones, too.