Winter's Splendor is a fun little module for the holiday season that has the advantage and disadvantage of being a holiday module and therefore feeling a bit out of place at any other time. However, it is a fun module and one with a few really standout moments, but also some issues that are a bit more difficult and perplexing to deal with.
First, let's talk about the good stuff. The setup has a wonderful mix of playful and sinister that works well together and the 'little child tricked by the devil' plot line is a classic story trope that players can easily lean into. It has great synergy with one season of Dragon Heist, really allowing you to get the players emotionally invested in some highly important NPCs, enough so that I'd be tempted to somehow integrate it into a play through of any Dragon Heist run I did with that season.
The tone here is great. Everything is a mix of creepy and cute, exemplified by the image of an imp in a Nutcracker outfit. Better yet, it builds well. The opening scene is pure holiday cheer. The performance is lovely until it isn't. The children's room is a scene of cuteness mixed with horrifying wrongness. (You can really do a lot with the imps going invisible here; have them manipulate toys and play it like a horror movie.) And then the graveyard scene is pure horror film aesthetic with no holiday spirit at all. Everything is placed well.
Bonus objective 1 is mostly a positive as well. It's a really fun, inventive scenario and certainly original. There is a drawback as well, though, which I'll get to later.
Finally, the puzzles are mostly very clear and well designed.
However, there are enough drawbacks here to cost it a star.
First, while not a huge deal, the first bonus objective is very dependent on a confident and performative DM. Are you prepared to sing at the table? Because while it's great, it only really comes alive if someone is prepared to sing. It can be a player or a DM, but it's really something you want to have happen, and not every table will have that. Bonus objective 2 doesn't have this problem but also feels very much like just a sequence of ability checks.
More of a problem is the ending. The shift to the location for the finale is somewhat poorly telegraphed and can easily slip by a party, requiring a fair amount of nudging from the DM. (Two groups I ran this for both came to the same wrong conclusion of where to go.) And the item required in the ending puzzle isn't in the adventure anywhere, meaning the DM needs to improvise a solution at the end. There's a few ways this could be done (make it easier by creating a quick location to purchase it, or make it hard by forcing the players into multiple fights as the time stretches on) with neither being wrong but both being sub-optimal.
Overall, I really like this module, but can't deny the ending lets it down a lot.