I went to a bootcamp two years ago.
TL;DR
Bad bootcamps are just like CS degrees from bad schools, they don't do much for you, though with a bad bootcamp you waste a ton less time and money. Good bootcamps get you job-ready, which I think few 4 year CS degrees can even claim to do. If you come into a bootcamp prepared (having been learning coding on your own for a minimum of a few months) then you should finish the bootcamp capable of getting a good job.
Rambling paragraphs:
Bootcamps are legit. They're not gonna produce deep knowledge in computer science, but then again most CS programs don't either even with four years. Bootcamps do get people job-ready a lot better than plenty of CS degrees do. Just like colleges, there are good ones and terrible ones.
I went back to school to study CS and by the time I was almost done I knew they had barely taught me anything for what I would actually need to know as a professional developer. And now that I am one, I can say I was absolutely right. It's shocking how little I was taught about what I would actually need to know even from Day 1 in the profession.
After college I started learning web development on my own then heard about bootcamps and realized that was exactly what I needed after wasting so much time and money on a crap CS program. Now granted, the Bootcamp I went to ended up not being very good at all, but after 2 months as a student and another two months as a teaching assistant there I was way more prepared to find a job (and did after a month of looking) than I was after going through school. And that was from a fairly bad bootcamp! By bad I just mean the instructor wasn't very good at teaching, plenty knowledgable just not good at teaching.
However, for most of the people that were in my cohort at the bootcamp, they didn't have a background like me in coding and they came out of the program barely knowing anything because it just moved way to fast for them. But thats because they didn't prepare properly. Combination of a bad instructor, the students not doing appropriate preparation coming in, and not continuing to work hard afterward in order to get a job caused some of them to have wasted their time and money.