I don't know if it's considered under rated but my favorite is Green Lantern (vol #4) when the Spectre goes against the Butcher, I think this comic has the best portrayal of Atrocitus showing what he stands for, specially with the conversation he had with the Spectre about Justice telling him how a criminal's life is worthless compared to that of an innocent, something many "heroes" like Superman or Batman fail to realize, to them all life is "precious" and "equal", even criminals. This is why I love Atrocitus so much, he has more depth than most characters. It's on DC Universe, I highly recommend it