An ex-colleague contacted me to come by for a happy hour.

I was impressed by the quality of the people there and the leadership.

The onsite involved a solid coding question requiring me to fill out the client-side business logic. The finished code was to be demoed (they had a server-side running already) and reviewed with a team member.

There were also a couple of algorithm questions.

Much of the interview also explored cultural fit, especially my interest in and thoughts on education in general. I'm guessing this was because I was interviewing for a lead (but not business development/executive) position.

I would not characterize the questions as difficult, so much as interesting and open-ended.