It might be very useful if TT problems were categorized by theme (e.g. pin, fork, discovered attack, deflection - some problems will have multiple themes). Then keep track of results by them so if it turns out that I frequently miss a particular theme I could concentrate on that kind of puzzle. I.e. the TT engine would choose more puzzles of the theme that I most miss. It would also help me to identify which tactics I should study more.

I have a modification of that request. I don't think it should show what the tactic is on the trainer, unless it was an option to turn it on (off by default). Then it could show the tactic when the puzzle is completed and maybe the site could keep track of the statistics for each tactic automatically that can be reviewed. In addition, have an option to just chose to play specific types of tactics so it would be self-driven training rather than automatic.