This review may contain spoilers. I can handle the truth.
The Guardians of the Galaxy were my first entry into the MCU, and I really enjoy their ensemble fun with planet hopping antics, comedy, and a good soundtrack. This side story was... okay. A cute little adventure, with some nice original songs, but not much substance. There isn't really much in the way of a conflict for very long. Problems resolve in about a minute.
So while I enjoyed the Christmasy spirit, and seeing how the Guardians celebrate the holidays, I didn't find this to be as exciting as it could have been. Still fun, but certainly not on par with the two feature-length films.