I enjoy them when there's DIY ingenuity and strong lore built around their plots. Effort and the devil in the details is really what makes it work for me. I remember "The Blair Witch Project" being one of the first things I ever deep dived into online as a teenager and I feel like participating in it's ARG elements gave me more context than the casual viewer who wondered why it ended so strangely. Should a movie require a homework assignment to enjoy it? no, but I think the digital bread crumbs of The Blair Witch went on to inspire movies like Cloverfield to do the same, and essentially created the youtube video genre of alternate reality gaming (which, like found footage, is hit or miss and your mileage may vary).
Is there more bad than good? Yeah, but that's true of any horror or straight up movie genre. To get back on the topic of what makes them good, I think there's a really weird punk rock parallel where the more movie studios get corporately involved and want to shill out more and more of these cheep horror movies (as they do with all horror movies) there's a diminishing return in storytelling, suspension of disbelief, and general interest. Is it possible to make a successful found footage style film with a decent budget? Yes. "Ghostwatch" comes to mind as a really successful TV movie that kind of forefather's the genre where BBC News just decided one night that they were going to shoot a fake horror story using real anchors. It kind of ends silly, perhaps to ensure the viewers at home understood that it was a giant H.G. Wellsian prank and not real news, but up until then it was played fairly straight, and in a way relying on non-actor types like news anchors to convey and narrate your story is kind of brilliant because they only know how to present like news casters and aren't going to overreach.
If I had any advice for anyone getting into found footage horror, it'd be to not watch the sequels. I might make an exception for Paranormal Activity because I genuinely liked the first two, but other than that just stay away from anything that has a number in the title. I'd also say avoid trailers, especially for [Rec]. Found footage is more about mood and atmosphere than jump scares, but a movie studio is going to put the few and far between big scares in the trailer. Also, check their rating on Rotten Tomatoes before watching. If it's above 50%, odds are it means found footage fans liked it and people who can't handle a shaky cam got pissed and left early.