Many of the negative comments about the James Bond films starring Sean Connery seem to stem from applying modern sensibilities to a product of the 1960s. It’s as if people are judging those older movies through a lens that wasn’t around when they were made. However, this particular film is simply not good. I feel comfortable saying that, even though Sean Connery is my preferred Bond and four out of his five films (I don't consider the sixth one) rank among my all-time favorites. The problem here is that Connery is portraying a character more in line with Roger Moore’s style—a lighter, almost comical 007—and it doesn’t suit him. The movie incorporates elements and patterns that would later become characteristic of the Moore era, but they don't mesh well when he's in the lead role. If *Diamonds Are Forever* had been a Roger Moore film, it probably wouldn't be so disappointing. It essentially is a Roger Moore Bond adventure, except with Connery instead, and that’s what makes it fail.

Source on TMDB