I think SS does some things very, very well, and some others are still on beta form. There´re two big aspects of the game that hurt the experience in a terrible way: collisons/physics and AI. The first wouldn´t be anything important if it wasn´t because the whole game is constructed around the main character having psi-powers. The physics don´t feel right, and the collision detection is lame. The AI is lacking. The guards will be seeing you act from afar and do nothing. Sometimes you can have a bin moving over their heads and they won´t react.
On the other hand, I like how the story is told and the conclusion is great. When you finish the game, everything takes a whole twist, nothing is like you thought it´d be. It´s one of the best executed twist I´ve seen in a videogame. And some moments are ace, so intense and unique that one feels sad that the whole game doesn´t keep up to that level. Using your powers in a creative way, getting through situations in different fashions, it´s all great. That´s why the game feels even worse, because you pass from an amazing situation to an embarrasing one, there´s no balance :-/
A big "it could´ve been great".