To opine about work you have not read...

... = utter horseshit.

Whether you opine enthusiastically or dismissively doesn't matter. (Though dismissing work you are in fact ignorant of is much easier, as you will not have to elaborate much or get very specific.)

This maxim applies whether are just some guy (or gal) with a blog, a really good poet with some kind of institutional platform, or even--perhaps especially--if you are one of our nation's leading literary critics.

i.e. we can tell you don't know what the hell you're talking about.

Uh, that makes you irrelevant.