This is one of the best FMs ever made, period, end of sentence. It's concentrated joy.

Warm fuzzies aren't a feeling that FMs typically stretch for, but AVTXMS proves that Thief's engine and overall nostalgic vibe pairs with those emotions like a fine wine, so much so that I found myself tearing up at multiple points. The narrative is wonderful; the reading of the cheesy Christmas poem is adorably hammy, and made my heart full.
But an unconventional narrative isn't all this mission has to offer, its level design is absolutely top notch as well! And of course that's the case, being it's from the creators of the Scarlet Cascabel, another all-timer in the Thief fan scene. The alleys and house interiors move together in a way that feels effortless and real, and the vibes are immaculate all the way through.
I also want to highlight the mission's STELLAR use of sound and music. The pockets of diegetic and non-diegetic sound, crowd chatter, caroling, and Christmas music that fade in and out as you weave through the City streets makes the mission feel more alive than just about any FM I've ever played, and I'm dozens deep at this point. It lends a cinematic quality as well, as if you're walking through a classic TV special that you've had on in the background of every Christmas of your life. There's one area, the church, that combines LD and atmospherics so effectively that I just sat there, in my warm cozy office on a snowy holiday evening, stewing in it for multiple minutes. Genuinely masterful stuff.

I'd say that the only thing the mission is missing is "MORE," but honestly, I think AVTXMS is the perfect size and length. It makes for a cozy 2 hour playthrough, 3 if you're taking your time/getting lost/searching to complete every optional objective.
If the authors want to come back and polish it up for a patched release with some fixed bugs (for example, the ambient room music overlaps with the monologue music in the Tiny Tim portion of the Christmas reading), maybe a couple minor additions (I want to frob and eat those green pastries at the end of the mission!), that'd be excellent... but if not, if this is the final version of the mission, well, it's already a 10/10, so I'll take it lol.

I'll be playing this every year around Christmas like clockwork. One of the best pieces of Christmas content any game has ever seen.