Should a paper be reviewed in entirety, if the introduction contains plagiarized passages?

I think you've pretty much done your review. You found a whole bunch of plagiarism up front, and that's enough to recommend rejection of the article. Document your findings and report to the editor. Even if the rest of the article turned out to be brilliant and original, there is no way it can be anything other than rejected and possibly even formal proceedings against the authors.

I can't believe that some of the answers and comments here are even discussing the possibility that a paper with plagiarized introduction may still be publishable if only it was otherwise brilliant and original. It's not like we assign 50% of the grade during review for brilliance, 30% for writing style, and 20% for not plagiarizing. It doesn't work that way: if you dope in the long-jump event, you're not getting a 30cm penalty for every jump -- you're kicked out of the event (and, in fact, banned for the next couple of years).

Plagiarism is not an offense that has to be balanced with the rest of the evidence. It leads to immediate rejection of the paper. In fact, I would suggest that the proper path is not even to just suggest to the editor to reject the paper (which is the same penalty as for the regular poor paper) but indeed to use an "exceptional exit path" (too much programming with throw-catch languages :-) in which the paper is rejected simply for plagiarism or unprofessional conduct.

See the Council of Science Editors white paper on publication ethics at:

http://www.councilscienceeditors.org/resource-library/editorial-policies/white-paper-on-publication-ethics/

and the Committee on Publication Ethics flow charts at

http://publicationethics.org/resources/flowcharts

Many journals follow these recommendations or similar ones in handling ethical issues.

As a reviewer, your job is to report this to the editor. The editor should take it from there.

I'm actually somewhat surprised that this paper even made it to the review stage- most publishers now routinely check all submitted papers for obvious plagiarism using tools that check against large databases of published papers and other material. Normally, this would have caught the kind of plagiarism you've described.