There are a ton of fun moments, from the Doctor doing a poor Sherlock Holmes impression, to Strax's encounter with a memory worm, to Clara continuously ignoring the Doctor's instructions. Even in an hour that's so dark, Doctor Who finds ways to keep its trademark humor.
Plus, the new TARDIS is stunning! It's a little confusing that the Doctor would switch designs mid-incarnation, however, given all that he's been through, I think a fresh start isn't out of the question. This new set will definitely help to convey that. I greatly appreciate that the series gives us a moment to admire it, rather than just glimpsing it while in use.
One thing some fans may have missed is that Clara works at a pub called "Rose and the Crown." During the Bad Wolf arc of the Doctor Who reboot, Rose and the Doctor meet Queen Victoria in 19th century England. This has to be connected to that.
"The Snowmen" is actually a prequel story to an old-school Doctor Who serial from the original run, in which the Great Intelligence attacks through the London Underground. So we get to see something that references a story many modern Who fans may not be familiar with. If the writers are lucky, this could open the door to new fans picking up the old serials.
Or it may just be the first of the many callbacks that will surely be referenced in the upcoming 50th Anniversary year.
All of which makes "The Snowmen" my favorite Doctor Who Christmas special thus far. Stellar job. Now I cannot wait for series seven to resume in the spring, a glimpse of the coming plot making anticipation soar so much higher than it already has, a considerable feat.