Hi DrSebWilkes, thanks so much for your feedback, while the Puzzles are different there IS still a way to tag a Puzzle with a 'Theme'
You can do this from a Puzzle you have completed if you go to your Stats and find the Puzzle,
Such as this one:https://www.chess.com/puzzles/problem/418151
Then click on "Themes" as shown here:
You will then see a drop down box where you can choose the theme that applies to this puzzle.
I hope this helps! Let me know if you have any further trouble!
There were a lot of issues with the old tags. What it needs is some kind of decent librarian to make the categories work better, and define them, and not let just anybody put any old tag on any old problem. Some categories need to be broad, and some categories need to be refinements of the broad categories. It would probably make some sense to have a computer rate the puzzles on a scale from simple to complex, from 'tactical' (meaning full of checks and captures and promotions) to 'quiescent' (more subtle or strategic, such as in endgame studies). Just before the "tags" went away, i noticed some additional tags had been added that made even less sense than the old tags.
I doubt "themes" are more well organized but I will be glad if they are ... I haven't looked at them yet ....
It's also possible that Machine Learning could look at human selections of Tags and figure out what a very good organizational system might be.
It is important to have categories because they definitely can improve the experience for users of learning.
I was going to post a topic on this but I see there is already one here so I decided to comment on this one.
So far all I have done is make comments on random puzzles.
Thanks for reading 
Sometimes I would use intuition to get an answer without being 100% sure if what I was doing was the right idea; either that or if I fail it's good to know what the puzzle was trying to exercise. Do think this should be brought back