It turns out that it ought to be titled Christmas Carols: The Gloomy Versions. They've made some very strange choices in the arrangements. Some of these can perhaps be put down to over-simplification: Coventry Carol, for instance, is in the key of C, which is Just Wrong. Some may be attributed to a Puritan spirit of solemnity and having no fun at all, or perhaps to simple ignorance of the songs in question: Go Tell It On The Mountain is made slow and melancholy by the simple expedient of writing every fourth measure to a completely wrong tune. Some are just inexplicable: God Rest Ye Merry Gentlemen traditionally ends the chorus ("tidings of comfort and joy") on an E. The arranger of the Peanuts Collection decided that one good strong note in both hands (as my old free arrangement has it) was too simple, and added a chord. This is all well and good. However, the chosen chord is E minor. E minor is not comfort and joy! E minor is afflictions and doom! E minor is sins and tribulations! E minor does not belong in my Christmas carols!
I didn't make it past God Rest Ye Merry Gentlemen. I switched to my other new book of carols, which seems much better so far. They're arranged as solos, so there aren't any printed words, they're substantially more difficult arrangements, they have lots of decorative flourishes, and they'll be harder to sing along with, but they sound good and they're not blatantly wrong. (Well, Coventry Carol's a bit cheerier than is really called for, but in a pretty way. I have not thoroughly investigated the rest of the selection; see also, substantially more difficult arrangements.)