Warriors Orochi 3, much like the rest of the series, is a tricky game to review. The concept is pretty straightforward, as I'll explain in a moment, but assessing its virtues is made somewhat complex by the fact that, on paper, it's kinda lame.
Repetitive in the extreme, it would be easy to write the game off as a disk unworthy of darkening your disk drive. For some, however, doing so would be a mistake, because although it is very definitely quite simple in design, the repetitive grind-like nature of the title can be quite compelling and addictive in its own right.
To start with, let me explain the basic concept. Taking control of a hero character, you enter into a massive open play area, populated by units of both your own and the enemy army. Your character can devastate massive swathes of basic enemy units without even breaking into a sweat, by way of simplistic, button-mashy combos. Occasionally, you'll encounter enemy heroes, and you'll need to take more care in your approach here, but otherwise the same spammy stuff ensues.
Your goal is to then use your hero (and you can switch between friendly heroes on the fly, making team selection a valid - if slight - strategic element) to clear the various objectives (usually a variant of kill X enemy hero in Y location) and win the level. Doing so advances the story (one of conquest, revenge, and fixing mistakes of the past) and unlocks more characters.
Each character has their own fighting style, with various strengths and weaknesses that you'll need to consider - along with your own preferences - when choosing your team before a fight. You can find new weapons for them while fighting, which - like the characters themselves - you can level up as you go. It's here that true fans of the series find their bread and butter as, much like pokemon, the real meat of the game is in finding and improving the huge cast of characters.
Presented in third person, you have full manual control of the camera with the right stick. Unfortunately, the game takes next to no control over the camera itself and repositioning it means taking your fingers away from the attack buttons. Given it's the kind of game that sees you changing the direction you're facing constantly, it's a bit of a chore and you end up just attacking straight into the camera (a sub-optimal situation) often as a result.
The game takes no advantage at all of the Wii U feature-set, presenting the entire game on both the TV and the controller at the same time, all the time. This does make it a game you can boot into without ever using the TV, but it would have been nice to have some sort of extra functionality available if you wanted to play on the big screen. The map is too small to be useful on the GamePad, too, so you end up just using it as a vague guide (kinda like Apple's mapping application).
Visually, it's nothing to write home about. It looks like a launch game, basically; it doesn't compete with any of the upper-echelon titles on any of the current-generation systems and has little in the way of effects layers, etc, to spice up the visual package. There's nothing wrong with it, either; a competent, if unexciting, presentation.
The same can be said of the game's sound effects; that it doesn't get too boring or repetitive, however, is testament to solid sound design - given how repetitive the actual gameplay is. You kill literally thousands of enemies every level, so it would be easy to imagine a sound scheme that would become painful to listen to quite quickly in that situation. It never does, however, so a pretty decent effort. The music is that typical Japanese Street-Fighter like orchestral stuff, which is pretty dated, but again, competent.
Competent sums it all up really. If you like the idea of an action RPG with a big emphasis on the action, lots of repetition, and game design that never quite achieves the entertainment level you think that it could, you'd be fairly well served by this. It's inoffensive and entertaining, if you like that sort of thing, and there's plenty of it.