Seems like a good price to me, and gives you time to complete it before the sequel is out later this year.
Game had a mixed reception, personally I feel it was slightly harshly treated due to the Gamespot controversy. Metacritic score is 67.
Next cheapest according to Gamestracker is 4.47 @ Tesco.
* A tense and unpredictable experience featuring two men who hate each other but must work together to save themselves and the ones they love
* Realistic and responsive environments and crowds react when things get out of hands. Manipulate the environments and crowds strategically to complete objectives
* Wide variety of intense 3rd person gameplay: rappel from buildings, fire from moving vehicles, launch surprise attacks, lay down cover fire, and shoot blind from around corners
* Lead a crew of criminal mercenaries to increase your chance of surviving and reaching your goals, or fight alone and your crew AI will automatically draw fire, throw grenades, and engage in close combat with their own signature moves
* Innovative multiplayer levels