I went on a lot of interviews (maybe close to 100) before starting my own business, and I'd say at least 9/10 of them were very positive.
By positive: I felt we both left the interview a bit happier than we went in. We both had a legitimate good time, and enjoyed it. It wasn't a grind, both people got to know each other.
I'd say I had a 10% offer rate. The most common "why didn't you select me?" follow up answer I got was "we need someone who is an expert in XYZ language." Sometimes it was even that they need someone who is an expert in ABC library (when I was already pretty-much an expert in the language.)
The ones that did lead to job offers I didn't want after the interview.
The other 1/10 was because they had me take an IQ test, or do some really super long project, or meet with literally all 20 people in the company, or they made me sit in the lobby for 2 hours past the meeting time.