Oscar Isaac did not receive an Oscar nomination for portraying Nathan Bateman in Ex Machina.
Oscar Isaac plays the role of the CEO Nathan, and really Oscar Isaac is a bit of chameleon as an actor. Not really in say the Gary Oldman fashion, but rather in the Masayuki Mori fashion. That being he really does not reinvent his accent or anything yet still seems so dissimilar from role to role. Take his output in 2015 for example where he was quite successful in being the hot shot action hero type in Star Wars: The Force Awakens as Poe Dameron, Though his accent is indeed the same he could seem more different as Nathan in this film. Isaac is a bit of a master in knowing how to carry himself differently, in again a very subtle way, yet the physical manner he takes with Nathan makes him seem like a wholly different person than the hot shot pilot from Star Wars. The funny thing both characters are even extroverts with Poe though he was directly extroverted, as in he was purposefully trying to make friends with anyone worthwhile, yet with Nathan Isaac does something very clever in that he's extroverted in a way that never quite seems entirely comfortable. Not that he's not really extroverted, he is, but the way Isaac presents does not make Nathan inherently likable.
Now there is something Isaac seems to be doing at the heart of his work, but I'll get to that later. In terms of the machinations of the plot though Nathan appears as though his constant is that of contradiction. In his very first scene Nathan is working out as well as drinking healthy liquids, but then proceeds to explain it as an attempt to recover from a severe hangover he has from drinking the night before. Isaac takes this idea to his creation of Nathan's personality in terms of his interactions with Caleb, and to a lesser extent his creation an android named Ava (Alicia Vikander). When Caleb first meets Nathan, Isaac plays it up giving Nathan a considerable charm, no doubt needed to be the head of a such a large company, as he suggests someone so excited to let someone else see what it is that he's created. The excitement in Nathan in the moment is extremely persuasive by Isaac as anyone probably would sign the ridiculous non-disclosure agreement that Caleb is forced to, since Isaac suggest only something unforgettable could possibly await. This is only made even easier as at this point, Isaac brings a considerable warmth as though Nathan really only simply wants Caleb to see this world changing invention.
However things begin to change when Caleb begins to conduct Turing tests to see whether or not Ava has true consciousness. From this point on Isaac never leaves Nathan as easy to decipher, instead being a bit of an enigma. There are moments where Nathan tells Caleb about how he actually developed Ava and in these moments Isaac exudes the needed smooth intelligence as well as proposes the sort of underlying passion that would be necessary for someone to create such a thing. Then at the same time whenever Caleb becomes too interested in merely the technical side of what makes Ava works, Isaac rejects the notion of the proper brilliant inventor. In these moments there is a dismissive tone that Isaac finds as though Nathan is almost holding his expertise above Caleb, and he does not want his input on the technical side of things since he does not need it. Isaac is terrific as he makes Nathan always slightly insulting in these moments not only because he seems to be stroking his ego to a certain extent, but also because he seems to purposefully try to turn Caleb's question against Caleb in some way. These are not jarring transitions but rather natural as Isaac presents Nathan as a genius, but does not feel like he always has to act like one.
Isaac is great though in the way he also plays with Nathan's relationship with Caleb, as he'll go like in that initial meeting where he seems to be quite encouraging, as well as seems to really believe in Caleb in some way. That's not always the case though as Caleb's own relationship with Ava continues to develop. Isaac though does not always keep this supportive attitude, especially when Nathan is drunk by making him not a particularly pleasant drunk to be around. However Nathan's nature goes even past this whenever he discusses the possible fate of Ava, and his own relationship with her. Isaac is able to be quite menacing here in a rather understated way as he suggests this certain darkness in Nathan whenever he directly deals with Ava, or it seems Caleb is becoming too concerned about her. Whenever Caleb tells Nathan a lie, Isaac creates this certain feeling of unease towards the film by indicating, mostly just through his reactions, that something is not right. As the film proceeds Isaac gradually makes this certain villainous side of Nathan grow as it slowly seems to become clear that he is the evil man that Ava claims that he is to Caleb.
Of course the masterstroke of this performance comes its revealing finale as the truth comes out about Nathan, that being the actual center of Isaac's work is around the fact that Nathan is just a BRO at heart. Isaac coalesces all lingering threads involving his character with this fact. His whole maniacal scientist routine was purposefully played up just to fool Caleb into helping Ava all the more. His ever changing mood, part put on, part standard potential moodiness of a true Bro. The reason this is behind all of behavior in some way is found in the revelation scene where Nathan shows what he had been up to all along. When he reveals that he's been duping Caleb Isaac is fantastic because he does not depict it as though he's an evil mastermind gloating about it, but rather is pretty casual in his explanation. Oscar's delivery is less "you were a pawn all along" to more of "sorry dude, but I had to make sure my A.I. pure". Of course him being a BRO was never hidden, with his constant dunking and the fact that he did not mind making a crude remark quite often. What I love though is Isaac in the end makes Nathan less than he might have been, but in the best way. He's technically more inconsiderate than outright maniacal My favorite moment in the film already gives this away, when Nathan breaks out into a surprise dance number. Technically Nathan could be doing his evil routine but at this point Isaac shows who Nathan really is as he'd rather just tear up the dance floor at this point. Isaac by embracing the BRO side to the extent that he does not only makes sense of the character's motivations throughout, but also makes this an extremely entertaining performance to watch. It's really a fun approach yet Isaac never compromises the tone or intensity of the film, but instead succeeds in only ever amplifying both.