The initial interview was a written technical test with a 2-hour limit (5 coding questions across 3 languages, plus an "optional" bonus question to be submitted after the time limit).

The next interview was a resume discussion with a manager that included some technical questions, but it was more of a screening (why this wasn't the first step, I don't know).

The final interview was a panel interview to go over my answers given in the written test.

Between the three interviews and working on the bonus question, I invested at least 10 hours of my time into the process.

I received a boilerplate rejection email a few days after the (seemingly successful) 3rd interview, and the recruiter would not provide feedback on why they did not want to proceed, which I found disappointing.

The position sounded like it would have been alright, but their people skills appear to be a bit lacking.

All of the 3rd interview had a theme of finding the "correct" solution, even though the questions had multiple candidate solutions that were equally valid.