I have been using the Goodreads website since 2008 with no problems and have rated 1282 books in that time. I use it mostly as I like to keep a record of what I have read. I use the star rating system so 1 means did not like it, 2 stars means it was ok, 3 I liked it, 4 really liked it, 5 stars it was amazing. Obviously it's down to personal taste and I probably rate most books as 2 or 3 stars with some 4 stars and an occasional 1 or 5.
I have received a message from an author of a book I rated recently that says "You have given my book a 2 star review. TAKE YOUR REVIEW DOWN NOW. You have no idea what this does to published authors."