Verbatim self-plagiarism in introductory sections

There seems to be no risk of getting credit twice for the same work here, as the papers are fundamentally different. It is possible that more modifications to these paragraphs would make them better suited for their role in the new paper, in which case suggesting that the authors do so is appropriate for the referee. However, rewriting the paragraphs just for the sake of it seems like a pointless endeavour. As a referee, you should not suggest that the authors waste their time on this.

On the level of research ethics, this is a gray area. While self-plagiarism is generally frowned upon as a breach of academic integrity, the degree of the violation in this case seems very mild. Unlike in the much more severe case of claiming double credit for the same results, the only double-credit taken is for coming up with the precise formulations in the manuscript.

On the level of style, copying entire paragraphs within an introduction seems lazy, an impression one wants to avoid -- if the authors took such short-cuts already on the first pages of their paper, what other short-cuts did they take? Rejecting an entire paper on the grounds of copied paragraphs might be a bit too harsh; requesting a revision might be justified.