I'd like a curve to track my progress.
I'd like to have the number of puzzles solved/failed.
I'd love to have my all time highest/lowest rating and so on.
The same stuff as you have for the other ratings. Statistics are nice.
I'm fully agree. I miss statistics for puzzles, that could be really amazing.
I wouldn't be interested in a progress graph since I know that how many tactics I solve right is more dependant on how much time I spend on each puzzle rather than my skill.
I would be interested what kind of tactics I have the most trouble with.
Some categories of puzzles that appear to be missing (some of which ought to be easy for computer to find in game positions, some not):
1. player is behind and would normally lose, but finds combo that forces draw by either stalemate or perpetual check.
2. combos that force a drawn (if would normally lose) or won tablebase endgame (or, perhaps, opponent can avoid those fates but only by incurring ruinous material loss or checkmate).
Present puzzle collection seems to be solely about winning (or not losing) material, and/or checkmate, which is too one-dimensional.