It may be unusual for a nominal American adult to have never seen an R-rated movie, but I think it would be even more unusual to decide, “Hey, let’s watch an R-rated movie!” just because one hadn’t seen one before. All the rating means is that this movie probably has some combination of graphic sex and / or violence and / or a lot of very coarse language. That may be due to the artistic requirements of the director and producer, or it may just be that the producer determined that the addition of gratuitous sex, violence and coarse language was required to make a marginal movie perform better at the box office.
In the past week I’ve re-watched As Good As It Gets and On Golden Pond, which are certainly not R-rated, but they’re among the best movies I’ve ever seen, and which I always appreciate.