This game is Tomb Raider meets Hitman. Throw in a great plot hook and you have a great game.
The environments are the best part of this game. There are tons of NPC's wandering around. The cities look and feel like real cities. I would play this game for a few hours if all I could do was walk around and admire the amount of detail that went into making this world.
The characters and voice acting are great as well. With the exception of one or two characters, nothing is done over the top. It feels right.
Everything plays right except for the end of this game. Don't worry, I am not giving up any spoilers in a review. The end seems as it was haphazardly thrown together. Why do game companies feel the need to not end a game they are going to make a sequel for? In the movies, it's no problem. Look at the Indiana Jones movies for example. You don't have to see all of them to get what is going on. They work as a group and they stand on their own. More games need to take this route. I was really frustrated with the ending of this game. There was no big bang for my $60 to get a sense of accomplishment. They could have taken this game 1 or 2 levels further and really ended it well, while also letting it lead into the next game. This really affects how I score this game. This game however, is worth playing all of the way through. It's just that fun.