If the plot was too hard to follow or didn't make sense I wouldn't put much stock in their review. If it simply horribly written with bad dialogue and bad prose then I am wouldn't bother reading it.

I read for enjoyment (at least fantasy novels) and I want to enjoy the whole book. I am willing to fight my way through a slow start but an interesting twist at the end doesn't make up for a long boring story and nothing makes up for bad writing.

I only find reviews of limited value anyways. I often see bad reviews of books I loved. Sometimes they are valid, The Lost Regiment was a horrible set of books that I loved and sometimes it is simply differing taste.