Shinobi could be considered a
Devil May Cry-style action game, but it stands out from that genre by shifting much of the challenge away from complex combat systems. Instead, it focuses the challenge on speedy maneuvers through 3D space and mastery of a relatively small moveset. In some ways it feels more like a hybrid of action games with 3D platformers, with long and challenging stages filled with bottomless pits and paths hidden beyond bridges of enemies to bounce across.
Your moveset - a basic slashing combo, a guard-breaking move, a ranged attack for stunning, a double jump, a dash, and 3 different one-time-use "smart bomb" style moves - is pretty small for the genre. But the moveset works in Shinobi's favor as every move has useful applications, and you will be required to make split-second decisions on what move fits the situation. Contrast this with other action games of the era, such as
God of War, which give you a larger list of weapons and combos but allow you to coast through the entire game consequence-free with just the two or three most spammable moves. There is some additional depth to the moveset though. The dash is a multipurpose move that can be used to speed through the stage, dash around an enemy's back, or act as an additional double jump that can be performed before or after the primary double jump. Speaking of the double jump, if you kill an enemy in the air you are given an additional dash and double jump which can be used to gain more height or distance and chain together multiple midair kills. You also are able to run along walls, which restricts you to back-and-forth movement but with most of the moves still usable.
Aside from the moveset, there are other mechanics at play which keep Shinobi moving at an intense pace. Your sword is cursed - if you go too long without killing any enemies, it begins to drain your health. This means you need to quickly make your way through any platforming segments in order to make your way to the next group of enemies to refill the timer on the sword. Your sword isn't just a curse though - it also becomes more powerful with each enemy that that you kill in a short period. Kill one enemy, and they are briefly frozen before falling. Each enemy that is frozen adds to your sword's power, which means its usually in your best interest to quickly identify the weakest enemies in a group and kill them before working up to the strongest. If you manage to kill every enemy in an area with a single chain, you are treated to a brief shot of your character sheathing their sword as the enemies all simultaneously split in half, and you are given a substantial boost to the sword's countdown to killing you. This also applies to the varied and interesting boss encounters at the end of each stage - nearly every boss in the game can be killed with one hit, but only if you can quickly chain together enough kills of the smaller summoned minions or projectiles, which leads to a delicate balancing act of allowing enough enemies into the arena to build a powerful chain without allowing them to overwhelm you with numbers. This system (known as Tate) in combination with the cursed sword timer are the main driving forces behind the game's momentum, and lead to many of the game's most interesting challenges. The timer on the sword pushes you to rush into combat encounters as quickly as possible, but the Tate system means you need to keep in mind the strength of all the enemies and plan out your next targets in the most effecient order, lest you end up in a situation where you are left against a group of strong enemies with no weaker enemies left alive to power up your sword.
To me, Shinobi is the best game on the Playstation 2, and the best game Sega ever developed, but it's understandable why it remains lesser-known. In reviews from 2002, it seems to have been dismissed for being too challenging and not technically impressive in an era where graphical advancement was prioritized even more than it is now. The graphics are fairly underrated though - while there certainly are a few monochromatic city stages in the game, there are also forests with blooming cherry blossoms and huge Japanese castles, and the main character's flowing scarf is one of the most visually interesting flairs on an action character that I've seen. The camera also seems to be a common complaint, but I'm not sure how it could be improved to suit the gameplay. You are given total control over the camera, meaning you will need to swing it around yourself or lock on to enemies, but I find this approach complimentary to the platforming and navigation-focused stage design, whereas more fixed or overhead cameras can have the problem of obscuring enemies or changing angles unexpectedly at certain points.
As for Shinobi's seemingly prohibitive challenge, there is very little tutorialization in the game which means that the game's Tate system could be missed entirely, but without knowledge of it it is likely that players would run into a brick wall in just a few stages. I could see someone putting the game away after having a frustrating experience with a boss taking upwards of 30 hits to kill, not being aware that the Tate system actually allows the boss to be killed in just a few hits with the right timing, or even in just one hit with total mastery. Once I understood this system I found that the game was one of the most thrilling I had every played, with every stage being a relentless sequence of varied and high-stakes challenges, whether you are flying through the air propelling yourself from demon to demon with your sword, or dodging around a pack of fast-moving ninja dogs in order to build up enough strength to slice a tank in half with one strike.