I think the challenges are a creative and cool way to get you to use some of the abilities that you may have overlooked in the main game. I don't fault the challenges themselves, although some are less interesting than others (I am looking at you, Bonfires). If you don't care about score or achievements than you will probably have some fun with these, especially at the low price point.
However, if you do care about score and especially achievements, then this DLC is absolutely dreadful. When you have a game that has achievements with a low-moderate level of difficulty and then tack on achievements that are as close to impossible as any achievement I have ever attempted, there is no other way to put it then to say that they fucked us. I've done Mile High Club (COD4), Hard to the Core (Dead Space 2), expert runs in L4D and L4D2, and completed Dark Souls with no complaint whatsoever. I enjoyed those challenges. These? These achievements are bullshit.
I have done all that I can stand with this DLC for now. I am walking away from the rest to wait to see if a patch comes out (highly doubtful), but I want to be sure before I devote the weeks it will take me to finish up this DLC.