Alright, I actually finished watching this series a couple of weeks ago so it is well beyond time that I wrote my final review of it.
Ataru may not be a perfect drama because when it misses it can be lackluster but when it hits it is solid. I do feel the worst of it is when the series tries too hard, such as the first episode and parts of the final episode. When it lets itself just go at a more natural pace and flow it works out well and avoids having things feel forced.
As for the mysteries I found they were more enjoyable when they focused on the people involved. They really were not ones that as a viewer you could figure out before the reveals, or at least not all of them, but instead they were engaging because you would care what happened to the people involved. For me this is fine as while it is best to have both elements having one or the other is good too, as long as it is done well. And the explanations for the mysteries made sense as well so that helped.
I did finish the drama wanting to see more and so glad there is more, even if it is not available subbed yet. But I am willing to wait as long as I need to for more of this series.