How detailed should my review of a very poorly-written manuscript be?
I view my job as a reviewer to be about triage and the "first order" issues with the manuscript.  Thus, for a very good manuscript, I will point out minor copy-editing issues, because those are the first-order issues remaining.  For a not-so-good manuscript, I will note if the manuscript needs language editing but focus on the scientific issues instead, because any specifics of copyediting are likely to be obsoleted in any case by the larger repairs that are necessary.