This survey will ask for general impressions on the game, and will also ask if the player feels that a level required skills from previous levels. Likely the most important fields in the survey, however, are ratings for difficulty and enjoyment. These are rated on a scale of 1-5 (5 being highest enjoyment, and highest difficulty. Also note that, arguably, ideal difficulty ratings are between 3 and 4 ('moderate' and 'difficult', where 5 is 'too difficult').
To remind players of the level I'm asking about in each section, I've provided an image. I hope this will be sufficient, and that players won't have trouble remembering 5 levels. Ideally, though, players would be rating each level immediately after they've completed a level.
With average difficulty and enjoyment ratings for each level, I'll be able to build an experience curve of my game.