I thought the first one was okay. Not "blow my socks off", not "this is revolutionary film-making that will show the way for modern horror", but... okay. Competent. At times, pretty well done. At times, effectively scary, and better, effectively creepy, which can be harder to pull off. Getting people to tense up isn't really that hard, but getting them to take the scenes seriously enough over time for an ongoing sense of dread to be created... that takes some work. And while you can prepare yourself for a "jump scare", you can't stay tense all the time, which is when an over-arching sense of doom becomes really effective.
But they kept making them, and while I've only seen bits of the sequels, everything I've seen has the term "diminishing returns" stamped all over it. At a basic level, once something is documented- which is what "found footage" films amount to- you need people to start having some basic awareness of the situation they're in. Otherwise, it's much harder to build that sense of doom for the need to roll your eyes at the people who keep showing stupid judgment.