I'm very rarely active in the forums on subjects like this so just for fun I thought I'd contribute a review ^-^'
I also have only sampled the album, as I'm very poor right now, but I'm confident in my knowledge of both their work and Yuki Kajiura's music in general to give what could pass as a rounded-enough opinion.
From Heaven Above
I'm a baritone singer in my college's chamber choir and I let our director hear both the iTunes sample and their tiny radio version, and she immediately changed our harmonies to it. The primary reason I follow Kajiura's vocal work religiously is because I am in absolute love with choir music. This made a very nice introductory piece.
In Dulci Jubilo
I personally love the waltzy feel that Kalafina provided, and was surprised at how much of the song was put onto Wakana's proverbial "back". It's not often that I heavily praise Wakana's work apart from the whole group because I kind of have a personal vendetta against sopranos and tenors in pop from any country (but especially Asia); however, this was damn impeccable work from her!
Fairytale
I must agree with several reviews from above and state that this ripped a bit too much from the original sound/version. I also hope rocks (or worse) aren't thrown at me for this, but I don't even like the original song very much so I was a bit disappointed that there wasn't really a progression to enjoy, like the kind they put into
Sprinter(!)
One or a few people may not have taken kindly to Hikaru cutting her lines but I LOVED AND LIVED for it. The original version, after years of listening to it, kind of makes me feel like it's a little too rock-ish for a little too long. Just me. This acoustic version puts in an entirely new mood, paints an entirely different destination in my head, and does it very attractively and successfully.
Jingle Bell
Just . . . what. I just had an open-mouthed smile on my face every time I listened to the sample! Gorgeous, I can't really find more than a description of my face to describe it!
We Wish You A Merry Christmas
As I said before, I don't regularly pay much attention to Wakana's vocal work when the whole group is singing at once. But when they went into "good tidings we bring...", my mouth was unashamedly agape in public once again. I enjoy the sound of the girls "feeding off" eachother during the lyrics, for lack of better words. I definitely will love the full.
KnGnN
Some listeners apparently thought this was too close a case to Fairytale in basically being ripped arrangement-wise from its studio predecessor, but I disagree. There are little details -- such as the verse vocals not sounding so staccato, and Wakana's falsetto end-of-verse inserts being absent -- that I personally enjoy and believe make the song sound different enough to be interesting.
Ring Your Bell
With two pastors for parents, I've been around forms of Christianity long enough that the original RYB always reminded me of a choral church song in a very good way. However, it also caused its accompanying PV to never truly fit in my mind. I always wanted them to have shot it inside a cathedral instead. This acoustic version absolutely fits their actual PV decision of a windy field. (My friend disagrees and sees the opposite.) (Sorry that's not a review of the song itself, but I'm an extremely visual person.)
Have Yourself A Merry Little Christmas
I enjoy when people I like make me a fan of something I wasn't a fan of before. I was never a huge fan of this song, and I love Christmas music. Personally, I particularly enjoy the harmony decisions made during the "Once again/faithful friends" sections.
Dolce
I know some review above mine droned on with claims that this song is consistently "forgettable" and I have to completely disagree, although I'm aware that the only backup I have to support my disagreement is the sheer joy of singing this song. The challenge of singing Keiko's part an octave lower than her really tells you if you're truly a bass or not! It is almost completely a chamber choir song in and of itself, and that's just the original version. This acoustic version is damn near orgasmic for me -- I don't know about the rest of you! XD
Alleluia
And once again (as in olden days), similar to my reaction to Sprinter, this acoustic Alleluia has revitalized my view of the song. I also enjoy the slightly slower pace, and agree with some others that it's a fairly wintery song. Keiko's tone pushes me to like this song as well.
Yasashii Uta
An observation above stated that this sounded like a song for the end of the holidays rather than the time it was released, and I do agree. In my opinion it's more of a New Year's, or honestly even a Graduation Ceremony song. Although I do like it a lot, I don't have much more of a descriptive view on it than this.