We assume that you don't rate puzzles that you haven't completed yet so you can view your TO-DO list by viewing those that are unrated.
On your profile page, we replaced the old style buttons with a single dropdown to give you more categories. This dorpdown tells you how many puzzles are in each category and when you select one, the list of puzzles will change. By selecting the UNRATED category, you can see what puzzles you still have in your TO-DO list.
Of course, this assumes you rate the puzzles you have already completed. Even though there is no requirement to rate your puzzles, If you don't, this category may not be very useful to you.
SUGGESTION: If you need to play catch-up on rating a large number of puzzles you have completed but you aren't totally sure how to rate them because it has been too long ago since you completed them, it would be best to rate everything right in the middle range so as not to sway the overall rating.