In a word: exhausting. I'm a bit torn between saying it was a good or bad experience. I met smart people, felt respected, had a wonderful recruiter, and I'm really happy in my position. That said, the process was incredibly long with many hurdles to jump. From what I hear this is not uncommon. I was sourced for a role early in the year, applied and finished the interview process in late spring (recruiter call, tech interview, design challenge, onsite) and then for a variety of reasons chose between teams in mid summer with fit calls.
The biggest surprise for me was that the process isn't really over even after you've passed the hiring committee. Depending on where you are in the year, your level, your area of expertise, your location -- you can float around in the pool of acceptable hires for a while (days to weeks to months) before team fit calls roll in without any guarantee of an offer. There is the chance that no fit calls will roll in, although I don't know that this is very common. While this was the case and isn't a secret, it's not stated very explicitly until you hit that stage, which I suppose makes sense as it could be demoralizing to work towards passing your onsite only to find you may not get an offer.
I'm not sure I've been here long enough to say whether the process is good or bad, but it's certainly a marathon not a sprint, and more mechanical than personal at many stages. Working here and on my particular team I feel I'm in a very warm, collaborative, balanced atmosphere, but that wasn't always evident in the hiring process.
That said, I felt like each stage and each person challenged me, and that's part of what attracted me. I'm grateful that it turned out to be worth it for me in the end, but it is, without question, a lot. If you're beginning the process the best advice I can give is know it will take a long time, and if you're dedicated to seeing it through then read up on people's medium posts, Google's "how we hire site" and values, watch their videos, check out the work and organization of designers you admire, do white-boarding and interview practice sessions with friends, and go in excited for the experience and learning opportunity regardless of whether you land the job. Even if I hadn't landed it on this go, it absolutely made me feel more confident and prepared in every interview with another company that followed.