What Do You Do If You Don't Like a Book? (or product or whatever?)

Today I read a review of a book that was just plain ugly.
The blogger obviously did not like the book. OK. Check. Got it. Not sayin' lie about it.
But goodness.
I have not read the book in question. I have read a lot of reviews about the book, though, and while none of them were a gushing recommendation, most were fairly positive.
I'll be the first to acknowledge tact is not a native characteristic for me, and I have been known to offend people with my opinions. I get being honest. But even I cringed for this poor author. The review was that brutal.
So what do you do? Do you try to find something positive to say? Do you say it wasn't for me, but if you like XYZ maybe it would be for you? Do you return it to the author/company & tell them you can't write a positive review for them? Or do you open up with both barrels & blast away?