Very sharp (smart) HR, brief phone interview.

Nice, swift hiring manager, half-hour phone interview.

Third step: onsite with engineers, architect, and upper managerial staff. Way nicer than what I expected reading Glassdoor reviews of other sites. The tech eval was a smart instantiation: "Look at this code and tell me what you see wrong." Plenty to spot that's wrong. Way less nerve-wracking than spontaneously whiteboarding a function that does X.

Technical detail questions, from your resume, from 10 to 15 years ago, in more detail than conceptual.

This position is well below your experience level; why are you interested in it? (I can only gather a company is unaware when they have premium work environments/staff.)