It's has a very nice passage when they get to singing about Christmas bells, and Bacharach wrote music that gives a lovely sense of cascading chimes. But the music is not especially singable, more "mood." Mostly however, this is not Hal David at his finest. I've never been a huge fan of his lyrics, but I've always admired the difficult job he had -- teamed with Burt Bacharach, who wrote highly-syncopated music, he was stuck with the uneviable task of making words fit with some semblance of sense, and generally did a respectable job. But here...?
Any song that begins, "Chistmas Day is here, and so are we," has a big hurdle to overcome, and it never gets there. Things aren't helped, either, by Bacharach rhythms that get David to put the emphasis on the wrong syllable of "happi-NESS' which alas sounds so forced that it takes me out of the spirit of the song, crammed for a rhyme. There's a sweetness to the song, but it just doesn't have enough to have become a classic -- or memorable. On the other hand, it's short.
Last comment --- the last 20 seconds of the song sound to me something out of A Charlie Brown Christmas. That's not a criticism (this came first, for what it's worth), just an observation.