I went into this after watching the anime adaptation, which turned out to be a good thing. The opening sequence of the anime is handled significantly better than it is in the manga--to the extent that, if I weren't familiar with the basic material already, I might not have pushed through that part. I don't want to do an entire review by way of comparison (especially since the manga is handling most other parts of the story better than the anime), so I'll summarize my issues with the beginning, then be done with it.
Simply put, the beginning of the manga feels rushed. It's like the author said, "Okay, you know this is an isekai--let's just get this guy to the other world, already." The back and forth between the protagonist and Being X is almost perfunctory in its brevity, whereas in the anime it felt a bit more ominous in how the protagonist's situation was drawn out, right before his death. Also, you never see Being X in the anime, leaving open the question of whether it really is the Abrahamic god it claims to be, or not. Here, it's very clearly a giant, old, bearded white dude, and putting a face to it makes it somehow less imposing.
That aside, the rest of this is really quite good. It takes awhile for Tanya to realize that Being X is still actively meddling in her fate, which makes her overconfidence and false sense of security at times seem more believable. Once she makes the connection, there's a subtle shift in her approach to her situation, away from prestige above all and toward establishing safety for herself first. I look forward to seeing how further interference from Being X will change her actions as the story goes on--because I've seen how the anime ends, and I really want to see how Tanya goes about executing her plan. But I'm getting ahead of myself.
This volume sets the stage nicely for the tale of a very unorthodox protagonist. Tanya starts out in the same mindset she had when she was a businessman in our world: rise up the hierarchy of society until you get to a comfortable position. But as the war rages on, she's gradually realizing she's in over her head, and I don't think it'll be long before true desperation starts setting in. I can't wait to see Tanya start prevailing against ever-longer odds. And the war, itself, is presented in exhaustive detail, from maps of troop maneuvers, to definitions of strategic terms, to combat and training exercises. I could see some finding it a bit dry, but I thought it was interesting.
One thing that I'm not sure I liked as much is the depiction of the gods. I mentioned Being X above, but...I don't want to exactly spoil this, but let's say Being X isn't alone up there. It presents a muddled cosmology, but also the potential for things to get even more complicated for Tanya as the story unfolds.