I've always liked this song. I think it has a very cozy, comforting feel to it which I like, and I think goes well with Christmas time.
You are right. It does exactly what a Christmas song should, evoke a positive feeling to match the season. It's like in The Lyrics where he said We All Stand Togethet was for those with young ears or something like that. Many critics make the mistake of listening to his music with the assumption that he is always striving for the next Hey Jude, Live and Let Die or whatever. Sir Paul is good enough to have produced an abundance of variety that needs to be appreciated for what it is.