2. I will review RPG books that I have not played. I am comfortable doing this for a few reasons: #1, I have a lot of experience in the hobby and am rarely surprised by what a game brings to the table. #2, it can be really difficult to get every aspect of a game, supplement, or scenario to a table. A single book can comprise dozens or even hundreds of hours of play time. #3, even if I were to exhaustively play out a book, due to the unique vagaries of individual groups and play sessions, it still wouldn't be a perfectly accurate assessment of how it would work for you and your group.
3. I don't use a 5- or 10-star scale for rating things, I use a Fudge scale. From best to worst, this is: