Suggestions- after solving a puzzle, show the percentage of people that got it right

that way the rating can be adjusted accordingly

What problem are you trying to solve?

Each puzzle has a rating which already reflects that indirectly.

Also, because of what @nadjarostowa says, the proportion of people getting each puzzle right should tend towards 50% anyway. So it won't be very valuable information.

EDIT: for clarification, another reason for this is that players are directed towards puzzles which are close to their own puzzle rating.
(When puzzles are chosen by the player, the effect won't take place. But most players just let the server choose for them.)