I was contacted by the recruiter to begin the process. The interview process was organized and efficient, with an initial chat with the recruiter plus subsequent logistical chats where needed over text and email. Then an initial interview / conversation with the hiring manager.
Then 3 hours of interviews in a day including an hour-long solution presentation to the hiring manager, one of his peers, and an individual contributor from the SE team, followed with an 1:1 interview/chat with that individual contributor, a 1:1 follow-up with the hiring manager (mostly review how the presentation went, which was short because it went well though I got some good feedback), and finally a follow-up with the recruiter.
After positive feedback from the recruiter and team, and overall good feelings about my chances, a few days later I had a final 30 minute conversation with someone in SE leadership to seal the deal
I say the overall difficulty was average because there were no obvious "gotcha" questions, and at the same time I was prepared for the individual interviews so they really were more like conversations about background, role, and fit. I also put in some good effort for the panel solutions presentation, so that helped. I presume that for someone who did not prepare, it would have been more difficult, but isn't that generally true in life?
To summarize, the recruiting team was great (organized, efficient, helpful, and friendly), and the hiring manager and his team were friendly and clearly like working with each other, speaking to a great company culture!
FullStory is clearly very well equipped with a great team and process for this phase of their growth!