I play a LOT of stealth-based games and Ronin has to be one of the worst I've ever experienced. It's sad too, because there's the framework here for a really good game, but it's destroyed by hideous controls and poor game mechanics.
What's so bad? Well, the controls are extremely wonky, in particular the grappling hook. Using it (and having it actually work properly) seems to be based more on haphazard clicking and luck. You'll experience a lot of misses and deaths due to the controls themselves.
The game gives very little indication when you're about to be killed. Sometimes the red reticle focused on you means you'll be killed or it simply means you're being targeted. The game makes more differentiation between the two, which is really, really annoying.
You'll only earn a skill point (something that's necessary to get new abilities) if you complete ALL the tasks in each level. This isn't bad in and of itself, but sometimes this makes for a no-win (or rather, no-earn) scenario where you need to choose between killing civilians or letting them ring the alarm. And no, sometimes it's impossible to avoid detection.
There's also relatively very little stealth in the game. It's more of a "kill-while-looking-cool" title, so if you want stealth, you might find this game lacking.
Perhaps the biggest sin of all is a complete absence of manual and quicksaves. You have to rely on (very poorly placed) auto-saves and checkpoints. This can be incredibly frustrating when you need to redo a bunch of stuff you did right in order to get to where you messed up.
So what's good? Well, the art style is neat and the game's requirements are extremely low, so any machine can run it. That's really all I can say that's positive.
In a nutshell, I'd strongly recommend staying away from Ronin unless you're a masochist. This game is unbelievably annoying and frustrating, not due to innate difficultly, but terrible game mechanics and controls.