unique experience
First of all, I loved the cel-shaded graphics which added to the grim nature of the game itself. It doesn't make the game more cartoony and that is good.
As for the gameplay, you'll get to acquire better weapons as you go along and store quite a number in your inventory. Best of all, you have different characters to toy around with and many side quests to level up your chosen character. The boss fights are also reasonable although not particularly difficult.
Overall, the concept of an RPG within an FPS (while not new) is a welcome break from the other top FPS titles that you are already acquainted with.