The major problem that most people have with this series stem from the false advertising associated with it. We were told multiple times that there would be complete answers by the end of summer, and let's just say that there were far more questions than answers, missing plot lines, and plenty of set up for some kind of sequel. Now, we look online and we find out that this was not a "mini-series" as it was billed, but instead, a first season. Add to this the fact that the show was often aired at different times each week, and that NBC completely missed airing one whole episode on TV, and you have one of the most messed-up releases of a new show that I've ever seen. That answers a few of the problems that can be attributed to the show, but certainly not all.
That being said, I was one of the few who tuned in weekly, and who saw the missing episode, and I have to say, I found this series rather intriguing. It works like a combination of "the Prisoner" and "Ten Little Indians" by Agatha Christie, or perhaps you're aware of the movie "Identity", which shared many of the little idiosyncrasies. Basically, it's a bunch of people who are kidnapped and put in a 1950's town, and you have to figure out just what's going on. Various obstacles are thrown their way, from the town randomly shutting down rooms and gassing the inhabitants, to the arrival of six body bags, which was supposed to cause them to start to figure out that only one of them was to be left alive at the end of all this. They try to escape, they try to fight back a bit, but we slowly see "the Program" slipping in and taking over for many of the characters.
There are some things that I still struggle with, even after watching the finale. A number of characters come back from the dead, some storylines tend to go nowhere, and as mentioned, there are very few definitive answers to be found. That said, I felt OK with the finale after learning that this was probably planned as a test run for a series, much like Lost. Anyone who has watched seasons of that knows that you don't solve much over the course of a single season, and yet that show garnered millions of viewers. If you liked that, you'll probably find something to like with Persons Unknown as well, albeit on a much smaller scale.
Overall, the show suffered from a few glaring plot holes, a bit of questionable storytelling, and occasional bad acting, but like I said, I tuned in to watch, every week, and as someone who has limited patience for television, that really says something. And if the show is lucky enough to come back again, hopefully with a little more advertising and a little more consistency from NBC, I'd be happy to watch it again, despite it's shortcomings.