The success of any memoir, in my opinion, comes down to whether or not I like the narrator. This goes beyond simple writing style - I can't stomach a lie or self-aggrandisement, even if it is well told. I'll be turned off by any hint of dishonesty in an autobiography. Unfortunately, that means I don't bother reading more than the first five pages of most memoirs.
Hard Time is the real deal. Attwood doesn't pull any punches. There are disgusting toilet moments, hideous descriptions of vile diseases, and tales of shocking negligence and brutality in the US prison system. Punishment, not rehabilitation, seems to be the name of the game there.
In some ways, Attwood was an ideal observer for this kind of thing. He was an outsider: not in any gangs, a foreigner, and well educated. In other words, he should've known better than to end up in the situation he was in. Fortunately, he never loses sight of that fact. Hard Time is as much about the other people he met in jail as it is about Attwood.
Read it, then read his blog for more.