I've been working on a PhD for mumble years now and I continue to have mixed feelings about it. My research is often rewarding and I like the niche I'm trying to make for myself in a couple different topics. I've learned a lot, significantly more than if I were to have gotten a job and tried to study on my own. I've enjoyed teaching and would love to continue.
But I don't know what I'm going to do when I leave. Having seen what is expected of professors -- I don't think I could do it, not without burning out long before I got tenure. Maybe at a liberal arts school where there's more emphasis on teaching and lower expectations for how much grant money you bring in, but that also means (from what I can see) less access to people with the skills to do the kind of mathematical research I like to do.
I'll probably end up in a national lab if I can manage a security clearance and stomach the additional pledge of allegiance to the US government.
I would definitely do grad school again if I was offered the choice, although I'd make some different choices about specific details. Aside from the job opportunities, I did it to satisfy my intellectual curiosity and that has made grad school "worth it" for me.
You didn't ask for it, but here's the one piece of advice I wish someone would have given me when I started: above all else, guard your mental (and physical) health. It only takes one or two bad semesters to really set you back. Without a doubt my failure to do so has added at least a year to my program, and I've seen people develop PTSD symptoms and not finish as a result.