I had originally decided to skip the Kage no Jitsuryokusha ni Naritakute! novels, as the premise sounded incredibly dumb. The Anime adaptation however ended up being good enough that I figured I’d check them out after all to see if any notable content was skipped.
Turns out the Anime is actually more fleshed out than the novels. There are a handful of things mentioned in them that it skips, but for the most part the novels are almost like a summary in comparison. Still, in a vacuum though I’d say the first two at least are worth reading if you like Overlord-y works… the third however is a different story.
The third doubles-down on the protagonist’s bizarre blindness to Shadow Garden’s activities to the point of contempt. Gamma literally had no issue giving him all their money earlier, yet he becomes fixated on scrounging for pocket change and just ignoring their accomplishments wholesale. It’s vaguely sickening.
So anyway, if you have a choice between the novels or Anime, stick with the latter since it’s the more refined of the two.