When I have writers block. I find it easier to break it into small parts. For example just concentrate on one section of the review then save it.
Also, it sometimes helps me to read other reviews. I see if there is something other reviewers haven't covered well or something I might have a different opinion on. I then get inspired or at least get a starting point. It is always harder for me to write reviews about mediocre toys. The really good and the really bad ones are just so much easier.
I usually start a review by thinking about what I wished I knew before I bought it, what I really liked, and what didn't work for me.