For starters, there's a proper plot and it's moving along at a good pace. No time is wasted on filler or tedious training sequences. The hero understands that rather than simply becoming stronger himself, he needs to build up influence over the humans' numerous kingdoms and get them to prepare for the upcoming war.
While armed with future knowledge, the hero is making his moves much earlier in the timeline, so he is often as surprised as the reader is. There are some subversions of expectations (like with the attempted assassination on the princess) that are really fun to read. He also eventually learns more about demons and their internal factions than in his first life, showing that things aren't as simple as he thought.
Enemies are usually handled ruthlessly, which makes sense given that he hero is a war veteran inside a younger body, but once again isn't something I expected to see in a manga like this. The party aren't beyond trickery and assassination either. This is not treated in an edgy, self-satisfied way, but like the necessity it it.
If I had any complaints, it's that the two female members of the party didn't get any spotlight after their recruitment. They're kind of... just there. In contrast, the hero's male friend is well-developed and in my opinion more interesting than the hero himself, so there's that.
