Satisfying in parts, but sadly held back by a lot of problems. It is a pretty poor PC-port in general - so expect things like controlling menus with your keyboard, or accepting option changes with enter and not being able to change most options while the game is running.
The game doesn't really know what it is: is it a shooter or a stealth game? It does neither with much competence and that's why it suffers. Many times I ended up being spotted even though I was hidden (as the game clearly indicated that I was) and other times when you'd think you'd be seen the AI seemed completely blind. The game just isn't very clear about if you're hidden or not.
These things become even more problematic when they start putting enemies in pitch-black rooms and have them directly face you, practically forcing you to take them out with gunshots in order to progress as they will never leave their spot.
To combat these gameplay contrivances, the game gives you two abilities: morphine and whistling. Morphine let's you essentially run up to fools and stab them without them being able to do anything about it. The risk-reward being you have to be sure you either have a way out of the situation that follows, or that the AI is the last in the immediate vicinity. If not, you'll be shot.
Morphine is limited and becomes a sort of "too good to use" item which I found myself only using if I knew there was another syringe earlier in the level so that I could backtrack and get it should I need to. This leaves the the "whistling" ability at your disposal, which is indeed very poorly implemented. Imagine whistling while being hidden and have a guard automagically aim directly at you, even through walls and cover, regardless if he's seen you or not, and get to a higher alert state while searching for you. Not great, but useful in some cases - at least when it works properly.
Because if you get shot, know that it's probably best to run away and hide though a door, as the checkpointing system is terrible and very unforgiving in places. More often than not you might find yourself re-doing the same sequence over and over using trial and error - which isn't very fun gameplay - or even just rushing to get to that next checkpoint because you really don't feel like doing that again.
I found myself sneaking my way through on my first attempt, getting really far, but when the game put me back several rooms or several minutes of gameplay in some cases, at least if you play it with stealth in mind - well I just lost my patience with it as you're litterally doing the exact same thing every time, so the more efficient way to get through it is to just rush through parts and skipping enemies everywhere you could, shooting your way through the rest, and completely skipping whatever collectibles were available as you need to pick them up every single time in case you die or reach one of the random fail-states that you can encounter. This style of play, of course, is penalized heavily as without the collectibles you can't upgrade your character, so you'll encounter harder resistance later on as you're unable to catch up to guards on patrols while sneaking and such.
There's no twitch-shooting or pinpoint accuracy here so don't get into it expecting a shooter either, but rather expect a 360 game that most likely had auto-aim to compensate for controllers, without the auto-aim component, so it just feels random instead. I frequently felt like I was aiming for heads but getting chest-shots, something which not only serves to alert other guards but also wastes precious ammo. A resource that seems critical in some sequences and indeed had me replay an entire level because I had run out of ammo at one point, before the game decided it was a good idea to put me in a brightly lit room with two soldiers and nowhere to hide.
Some of the stealth take-downs are quite satisfying however and I personally liked infiltrating places wearing SS-uniforms even though that stuff could also have been done better.
All in all, an OK game to get on a sale as long as you get into it expecting it to be wonky.