I found both kills to be very enjoyable and cathartic. Its the dialogue. Yeah they could have given Gemini killers a little more pizazz and made them harder kills, but instead we are just seeing prime Dexter entering the lions den and revealing the lions to be cubs. They just dont measure up to the experience Dexter has in hunting killers.  The dialogue and acting is just so good. Dexter gives himself the spiked drink believing that Gemini, who believes himself the smartest in every room, will likely insist on switching the drinks to show how intelligent and prepared he is. Make no mistake it was a gambit, and Dexter is both relieved and proud that he called it correctly.  And then the way he taunts the twin at the island is also really great performance. The tension rises over time as Dexter goes back and forth revealing that he knows Geminis secret, but dont worry he wont share it with anyone, but also I know about your notes in the bookstore, but its ok I was just following because Im such a fan, but actually do twins really feel each others pain? How about last night, when I murdered your brother? Just a chefs kiss moment of expertly taunting a serial killer to lose his cool and go on the attack.