I have pretty much listened to every episode of Hardcore History, as I also am not a historian I can't give you any help on how well done the research is. But I could give you some directions to the according to me really great episodes.
Ghosts of the Ostfront- A multiple episode series about the eastern front of Germany during WW2. This series really chilled me to the bone, even though I live in Sweden the education you receive about atrocities that occurred just a few hours away from me is minimal, the rape of Prussia and the mass killings of russians so that the germans could take the land for themselves after the war for example. Just in general how close it really was that Germany defeated Soviet Russia. And had they done so nothing would have stopped them, 95% of all german casualties happened on the eastern front.
Fall of Ninevah- An episode about the fall of the Syrian empire and especially the city of Ninevah. Again something that I had no idea about, he does make some good points about how every civilization thinks it's gonna last forever. The Assyrians sure did so.
Punic Nightmares- A detailed walkthrough of the three punic wars between Carthage and Rome. It was these wars that would cement the rise of the roman empire as the main power of the Mediterranean as after the destruction of Carthage during the third war there was no other power left to really confront them. Follows the same style as the fall of rome series and I would think is as accurate as it needs to be, needs to be taken in account that the people writing this down was probably trying to shine a positive light on Rome, even though the third war was just them mass murdering all remaining citizens of Carthage so that they never would threaten Rome again.
The new series about the mongols is also definitely worth a shot. Still as I am not an historian but just interested in history I can not tell you anything about the accuracy of facts but nonetheless it has been very interesting so far. Had no idea about the happenings of the mongol invasion of the muslim world for example.