Let's separate two things: the job, and the interview process. The job (and the company, for what matters) seemed fine, and I actually think I'd have enjoyed working with some of the people I talked to.
My problem was actually with the whole process. At first I had a phone call which turned out to be a technical challenge, something which I wasn't aware of, and I actually had allocated some time only for talking with the HR person, certainly not for an hour-long technical challenge as well.
Throughout the whole process, there were 3 instances where I was the one waiting for an email or a phone call, but I always ended up soliciting for a reply. I understand that delays may happen, but keeping the person in the dark is the absolute worst way of dealing with this. It's a matter of principle.
Finally, my in-person interview started with a 45-minute delay. If I hadn't traveled a few hours to get to the company's office, I would have left. That is no way to treat a candidate. I wasn't even admitted inside the company's office, I was left in the building's lobby.
All these things to me signal a disrespect towards the candidate. It may have been an extremely unlucky sequence of events, but now this doesn't certainly make me want to work for this company. And that's a pity, because the actual job and the people I'd actually work with seemed perfectly fine, but I can't in good conscience decide to accept an offer that comes from a person who cares so little about candidates.
My guess is that this person is used to dealing with candidates who actually need the job, and therefore are ok with being treated a bit poorly in order to get to the job. Thankfully I'm not in such position, so I declined the offer.