I've watched both the animation and the movie, as well as started reading the manga a few weeks ago.
!! I'll assume that most of you reading this have seen the Anime & Movie, and perhaps read the manga.
THIS WILL CONTAIN SPOILERS ACCORDINGLY !!
Having said that, it'll bring me to the most important part about the novel in case you are interested:
Both the Anime and especially the Manga have a much bigger focus on action and if that is one of your necessities, chances are that you'll be bored by the novel. A large part of it is Tanya's internal monologues and going into detail over her plans, actions and general historical strategy & strategists (obligatory mention of Sun Tzu). You'll even have your fair share of economical concepts talked about. And of course coffee (not even joking, I stopped counting the amount of times Tanya was confessing her love of it, thanks Carlo Zen). Nonetheless the novel doesn't lose its sense of humor, which I really appreciate. For example, Tanya even mentions how she tries to add jokes to her conversations when speaking to her battalion, and sometimes fails miserably at it because they don't catch onto her sarcasm. It shows nicely how little empathy she really has, and how much of her interaction is what she thinks are social norms. Over time, she warms up to her battalion though, and I like to think she's developing some humanity.
A lot of the wickedness/edginess of her character isn't so emphasized in the novel (especially in comparison to the manga), and during the majority of the time, you will be witnessing her cold and opportunistic character over anything else. As mentioned in another review on here, a large part about her "evil" stems from her treating war as a clash of human capital. In her own mind, she is simply being efficient and expects everyone else to think the same way. So while in anime and manga she is portrayed as a maliciously evil (for example the pill bunker at the very beginning of the rhine front & her sadistic smile), the novel makes it quite apparent that she's just doing what she considers efficient. People want to die? Sure, she'll give them opportunity to die in a way so she isn't handicapped by it.
She quickly earns herself the reputation of a cruel warmonger because of the way she prioritizes efficiency over morality. This is motivated by her desire to get off the frontlines as fast as possible, ironically resulting in her being sent there over and over again. So whenever she gets an easy job, she beams with happiness and people around her think that she's thirsty for war, resulting in an even worse reputation. She's pretty much oblivious to this as well. It's why I find it misleading to actually call her a sadist.
Overall, I believe that Carlo Zen sort of lost sight of what he was trying to achieve with this novel. He wanted to make knowledge of WWI more appealing to the japanese, since it's not a well known subject in Japan, which I think he does a fair job of. On the other hand, he was trying to show the flaws of Fascism (with alter-germany), but their success makes this questionnable. And with Tanya, he wanted to have an unlikable main character, by whose suffering you were supposed to be amused. With her unconvential personality and Mary-Sue characteristic, I think he achieved the exact opposite, simply judging by her popularity alone.
tl;dr
the novel has a heavy emphasis on strategy, history and some economics at the cost of being less action oriented. Tanya's character is more fleshed out and less cartoon-ishly evil, as some scenes in the anime and manga might suggest.
Might also be worth mentioning that the novel and the anime have quite some differences in their story, which will be very apparent when reading it.
few examples: Anton Sue's death is during a mission which is not even covered in the anime. Neumann and König basically don't exist in the novel (at least up until book 7), only Grantz, Weiss and Visha are "main characters" of the Battalion. there's a lot more but you get the idea.
Personally, I very much enjoy the novel and am excited about the next book.
If you disagree about anything, or think I'm misrepresenting something, feel free to send me a message
