At first this game started out slow and I really didn't like it. If you are use to playing 1st person shooters where your accuracy is always 100%, you will probably get frustrated at first. Once you get use to the accuracy of the guns this game is amazing. It is one of the most immersive 1st person shooters I have played.
The other really great thing about this game is the history. All the bonus content is actually interesting for once. Most games unlock concept art and stuff but this one gives actual documented history on the real life story that the game is based on.