The Joker Game novels were actually collections of short stories to start with: the guy doesn't write ongoing series, he does single novels and short stories only, in the detective, mystery and thriller genres. So while there might be common characters in Joker Game, each story is a standalone "case".
So yeah, of course it won't feel like there's any overarching plotline, because the writer didn't set out to do that. Probably, what anime viewers are seeing as a lackluster "story" is the anime producer's attempt to turn a pile of loosely-connected short stories into a continuous "saga": someone who wasn't the author has basically come along and faked continuity where there was none.
This works a bit better for light novels / complete novels, because one LN will generally map to 4-6 anime episodes, so you only get a "reset" every ~4 episodes. A Certain Magical Index and Strike The Blood are two similar anime in this regard. You have the "daily life" start of each arc, the bad guys turn up, ups and downs, then the big takedown in episode 4 of the arc. Then, at the start of the next episode it's back to the "quiet daily life" part. But with novels that are made up of 3-6 disconnected stories, such as Joker Game, then there's not a lot you can do but 1 episode per story.