Said to be the best adaptation of a Type-Moon work ever, I decided to get the first five volumes, since volume 6 is rare and expensive at the moment. I've done a review of it on MAL, now it's time for me to go into spoiler territory.
First off, I said it was more visual than the VN. For instance, when Nanaya cuts Arcueid into 17 pieces, you actually see what Arc looks like in that state; perfectly cut up into 17 beautiful pieces. And also, the "nod" to Kagetsu Tohya I mentioned is that during what would be the first "H" scene in the game, (He chooses Arc in the manga) after his . . . what have you (which is edited out), you can see a black cat with a large ribbon slipping out when he wakes up. Things like that will please long-time fans.And also, there are new scenes not from the VN which thankfully don't feel out of place. One of which is a fight scene between Ciel and Akiha, but man, Akiha can pwn in the manga! Her demon powers are better illustrated in the manga than they were in the VN. Another interesting change is the place where Shiki was nearly killed by the other Shiki has a gazebo standing where that happened; it's not just a shadeless spot in the woods anymore.
However, I caught a few plot holes in this canon. For one, Nanaya doesn't 'kill' Arc in her apartment, but rather, at the park, right after he first sees her. Um, dude, that's a public place and it was during daytime; did no one see him doing that? And also, maybe it's just that I haven't gotten past the fifth volume, but Sacchin isn't a vampire, Hisui hasn't revealed that she used to interact with the Tohnos as a child, and nothing has been mentioned of Kohaku's true self. Also, Kohaku doesn't give Shiki the Nanaya blade, since he already had it from the start; isn't the reason she handed him the blade in the VN is so he would draw out and and possibly kill the other Shiki? I can excuse the not giving the knife part, but the other ones are holes that better be paved over in later chapters, but I have faith in whoever's writing this.
Oh, also, there's an interesting bit of fanservice in the third volume. There's a colored illustration of the girls in a spa, but it includes characters that don't appear in the original Tsukihime VN, such as Seven, the human form of Len, and even Miyako from Melty Blood! Truly fanservice; a newcome to Tsukihime wouldn't know who those people were!
But other than all of that, I have another confession; I mentioned that Arc has nice eyes. I guess I should say now that crimson red is my third-favorite eye color. Yeah, I know it's fake, but I can't help myself!