I think OHMSS is probably the biggest gem in the Bond-catalogue and used to be overlooked and made fun of, but I think the more time has passed, the more people have started to appreciate it. When I was young, my parents always made fun of OHMSS, my dad loving the Moore-bond and my mom loving the Connery-bond, and they both joked about Lazenby being "too bad to make another one". I bought into that as a kid, because knowing the others had made several films, it came off as a failure that this guy only made ONE, and then was replaced. As I got older I learned more about the story behind it, why he didn't return, and it was one of the last Bond-films I saw out of the pre-Craig ones, and it's actually really good.
As much as I appreciate all eras of Bond, OHMSS would be in my top5 Bond films. I think there are some rose tinted glasses involved and I don't think my example with my parents is unusual, I think a lot of people dismiss Lazenby and OHMSS simply because it's the one-off film.