A Shooter with RPG elements is the best way to decribe this game. You will love the stealth experience.
Adam Jensen, the games protagonist, is a security chief at a large Human Technological Advancement Corp(HTA.) called Sarif Industries. His life gets turned upside down one day when Sarif Industries is attacked, and to save his life, his boss, Sarif himself, gives Jensen the best augmentations Sarif Corp. has ever created. The rest of the game is all about Adam Jensen searching for the people responsible for the attack, and the death of his ex-girlfriend.
The most important aspect of the main story, is the use of the HTA augmentations and morals of augmenting the human body, replacing limbs with mechanics. This will raise moral, religious and political questions from all sides, questions that will affect the player personally, if you let it. The characters are very believable and realistic, but none of their background stories will be explored, namely because this is more of a Shooter with Role playing elements, rather than the opposite.
The FPS element is even better than in the Fallout series, and the Stealth moves are fantastic, some of the best i've seen, and there are lot's of stealth games on the market. The use of augmentations to enhance abilities, and give you new ones, is a great way of combining a Shooter and RPG experience.
This game is great for all Shooter and Stealth lovers out there, but RPG fans will feel a bit left out when it comes to story and characterisation.
If you liked Mass Effect( or Alpha Protocol even a little) then you will love this game.