I won't comment on the gameplay, graphics, story, etc, because I think the existing user created reviews cover those quite well. In a nutshell, they range from OK (but not great) to poor.
However, I think the 'special something' that Mindjack definitely has is the jump-in/jump-out feature which allows you to either fight alongside or against other Players in their campaign. In my very first play session, I found myself fighting against other Players, which provided a really fascinating experience because it prevented the combat from becoming stale or predictable. I later tried joining other peoples games, and had a lot of fun both as an ally and as the opposition. I can see myself popping into this game for some co-op fun every once in a while, even after I've finished it.
In short, for the low price, I would recommend getting this game if the above sounds intriguing for you. What have you got to lose apart from the price of a Whopper Meal? :-)