I think it's about time I clear up for myself the difference between these various synonyms:
Preserves: the most general term, refers to preparations of fruits or vegetables with sugar.
Jelly: derived from fruit, using the natural (or added) pectin of the fruit, typically without the flesh of the fruit.
Jam: derived from fruit, but with juice and flesh of the fruit involved.
Marmalade: made from citrus fruits, and includes the peel of the fruit.
All clear? I like a puzzle that makes me look something up. And I also like a puzzle where a straightforward theme like this one is not spelled out through an unnecessary revealer. I'm not sure why this puzzle took longer than typical for me to finish (for a Wednesday, anyway). It's got lovely open sections in the SW and SE corners with a total of eight down entries of 8 letters or longer, and each of those answers are really strong, in my opinion.
VOLTEFACE is great, PILASTERS is very nice. I love UPBRAIDED. And how about BERYLLIUM? Pretty impressive group of answers. I will say that 13D: Cons (PRISONERS) is slightly off, because not every member of one group is a member of the other group, or vice versa.
On the negative side, I don't like ECOLAW (doesn't google at all), and IRATER is unpleasant as well. 1A: Gift from 1-Down (SLED) is not great, in that it's an immediate cross-reference. I don't like having to look elsewhere on the very first answer in the puzzle. I'll give it a D+ for that reason. And then, wouldn't you say that SANTA's primary relationship to SLED is not one of giver, but one of rider?
It would have been fun to see 19A: Robin Hood's target (THERICH) clued in some way referring to Donald Drumpf (such as: Candidate's true constituency).