I really, really want to love We Know the Devil, but as it stands it takes some excellent ideas and executes them poorly. It's worth picking up, especially if you have a personal investment in some of the themes regarding social interaction and group dynamics which it discusses, but it doesn't raise any especially interesting questions that aren't better handled by other fiction. I at least hope that We Know the Devil can be a stepping stone and an inspiration for some to dig deeper into important questions for themselves, so I guess that in of itself has merit.
If you're interested solely in entertainment value, and don't have a particular reason for exploring this abstract sort of horror, there are probably more appropriate options available.