I highly doubt that was true 40-50 years ago. Although I don't doubt they at least had a good view of it. Hadn't gotten the impression critics "hated" it, just that it wasn't the darling that Paris was. After all, Paris won *Best Picture* and Rain wasn't even nominated. That's telling right there.
They didn't hate it. It's just not regarded as all it was cracked to be at the time. And Oscars are strictly a Hollywood thing. Critics don't get a vote.