I think I enjoyed this one exactly for the same reasons everyone disliked it: the characters were so messed up it was nerve-wreaking to read.
I've likely commented many times before how I love those books that engage me enough for me to get emotional over the characters, even if it is rage enough to want to strangle them, and that's pretty much what happens here. Bruno is a messed up cookie, and Guy is a derrotist moron, and that's what drives the slide-down-the-slope plot.
There is the thing too. I think most people think this will be something that is not. It is not a mystery. It is not a heist type of book of two guys planning perfect murders. What it is, is the very, very, very messed up relationship between a sociopath and a coward. The murders are just the thing that binds them and the theme is something like "all the wrong choices". While it made most dislike the book, it made me want to bitch-slap Guy and continue to read the train-wreak.
I think Highsmith was trying for this high-minded "either guilt or law will punish" poetic thing at the end, but it felt like an unnecessary convolution that made me go "NOW you find your spine/brain/cold-thinking to live with your actions, you moron", which, yeah, OK, poetic irony or something but... 4 stars