What should I remove to make my reviews less spoilery?
I recently received a comment/complaint on GR that one of my reviews was too spoilery.  (Well, I think. The comment wasn't very clear.) Unfortunately, the commentor didn't give any details about what aspect(s) of the review were spoilery, so now I'm left in a mild panic over the Unknown.
In terms of my personal concept of "spoilery," the review in question was okay because it didn't contain any plot details, but I really think my definition is far too liberal.  I would definitely prefer to err on the conservative side, and I'm clearly failing there. Although events are pretty easy, I think I have trouble looking backwards over the book and deciding what themes and character descriptions count as spoilers.
So please, what should I be hiding?  I won't take suggestions as "criticism" or anything--decreasing my in-review spoilers will have essentially no impact on my enjoyment in reviewing because I'll just put more stuff behind spoilertags. (This would have the indirect benefit of making my reviews shorter, btw.)  If the spoilers are absolutely inextricable from the review, I could just tag them with the big red spoiler-tag, although I really would prefer to not do that.
TL;DR:  I am very, very willing to hide more spoilers, but I don't know what I should be hiding.
What should I be spoiler-tagging?  
Character descriptions?  
Comments about characters' personalities? 
Comments about book themes?
Something else?
P.S.-- when you do run across something in a specific review you think I should hide, please, please, please let me know.  I promise I won't take it as criticism or be offended, and you'll be assisting anyone else who might stumble over the post.