The game itself is not bad. I've found it decently enjoyable. Not a huge amount of replay value, but I got to the end once. The problem with Paranautical Activity is the developer.
The developers have continuously insulted and mocked people who bought their game. In addition, they have been less than honest. The game was marketed for over a year as having co-op incoming (and as of this review, the store page says the developers are still working on it), yet that feature was suddenly canceled. The developers insist they have been working hard on bugfixes and content updates, yet have not released anything, even missing a promised deadline by over two months (patch is yet to be released as of this review). Furthermore, the devs have been silent on the forums (when not aggresively insulting the people who bought their game) and insist you should visit their website, where they will keep people updated; visiting their webiste reveals no new news in two months, and the last message was just an apology for a delay (that has still not been resolved). And when fans have the nerve to say they aren't being treated fairly? The devs say people are "entitled." Do not buy this game, do not support this kind of rude immaturity from developers, do not support Early Access games that are deceptively marketed.